Why does the Clarion 2001 have a left and right channel input if the output is mono?

Auxiliary output sockets (AUX 1-6) would usually be used for connecting to an FX unit input, with the signal levels sent to the FX unit governed by the AUX SEND pots from each input channel, setting the AUX MASTER at a level that will prevent peak signals from the various channels (sent to the FX unit) from clipping the AUX bus rails.
The output of your FX unit can be then be returned to stereo line input sockets (ST1-4).
For details see the GL2400 User Guide:
AUX OUT 1-6 (p.15),
AUX SENDS (p.17/18),
AUX MASTERS (p.19),
STEREO CHANNEL LINE IN (p.14).
If you require more precise EQ parameter control of FX return signals - and you have sufficient spare channels on the desk, connect to 2 x mono channel inputs:
one from left FX return, one from right FX return, with each of the console's input channels panned hard-left/hard-right (this assumes the FX unit has a stereo return).

first this needs to know if set has internal left and right speakers

If you are saying that it only works on say the left channel in stereo mode, but both channels come on in mono, then there's a fault in the amplifier's pre-amp. These days they are an IC, it can be traced by following the input wires to the point on the PC Board and then looking around for an IC with all inputs going in. If you are lucky there might be two! One for each channel. Replace the one on the dead channel. You can test it, either the single IC or both, touching it's pins with an insulated tool while the amp is on. It will buzz on the channel. Stereo amps have two sets of identical parts, except when an IC is involved. But even then that will have two halves (inside it). You just need to touch the pins of the IC, with the tool, but don't short the pins together! You should hear at least 4 buzzers. One at the right input, one at the left input, one each at the left and right output. If you only get the left an right output buzz, plus the good channel input buzz, you know it's the IC that's gone.

The "Front output" from the Pioneer deck would connect to the "Main In" on the Clarion EQ. I'm assuming that your Clarion EQ can only deal with one input, and will send the adjusted (equalized) signal out both of the outputs.
The "Front output" from the Clarion EQ should go to the "Front Input" on the 4 channel amp.
The "Rear output" from the Clarion EQ should go to the "Rear Input" on the 4 channel amp.
The "Sub output" from the Pioneer deck would connect to the Left/Right Input on the Epicenter. The Left/Right Output on the Epicenter would need a Y-splitter for each side, so that you could connect each amp separately. One suggestion would be to use one sub amp for both subs.

Hi,
I assume english is not your first language, but I think I understand you.

Right first thing is, yes it is marked. You connect the MAIN/Master outputs marked L and R to your amplifier. The tape input is marked L & R too. The stereo channels will be mark L and R but the numbered channels are mono and as we all learnt in our first mixer lesson, to make a stereo you plug left into channel one and right into channel two then pan channel 1 hard left and channel 2 hard right.
If you use a mono source such as a microphone and you want it to come out of both speakers, put the pan control in the center.

Just for clarity, I need to explain what the four inputs are on the KEF subwoofer. There is a left and right RCA input which is the input signal to the subwoofer and there is a left and right RCA output which is the High Pass output from the subwoofer.

On the back of the Yamaha receiver, you said you have a subwoofer output. This output is most likely the mono subwoofer part of the home theater system and can be used if you like. The left right signal input into the KEF is summed into mono so if you only connect one channel you will basically reduce the signal level by 1/2 (-3dB) but it will work fine.

Alternatively, if your Yamaha receiver has monitor out and monitor in, you can run the monitor output signals to the subwoofer and you can then run the high pass outputs from the subwoofer back to the monitor in. This will give you the subwoofer and provide a smoother signal matching with your audio system.

It is not always easy to connect the subwoofer up to an integrated receiver/home cinema system using the high pass channels of the subwoofer as you don't always have access to the analog output and input of the front channels. In this case, just use the Subwoofer output or just the monitor out only.

I hope this solution is helpful.

You can't convert mono to stereo since the TV only has a single input, and not the separate right and left channel circuits needed for stereo. If you are connecting a stereo source like a DVD player, what you can do is combine the right and left channels into one and connect that to the mono input. You need an audio Y-adapter with two RCA jacks going into a single RCA plug. These are available from Radio Shack. If you are outside the US, there should be local sources such as a stereo shop where you can find the adapter. This won't give you stereo, obviously, but you will have all the sound.

It's unclear what type of connectors are on the end of the cables(s) coming from your computer.

This amp only works with mono 1/4" TRS and XLR connectors, not standard RCA connectors.

Did you try the Right one in the Left Channel to see if the Left Channel worked?

Refer to the following manual and read up on the connectors (page 7) and the use of the Stereo/Parallel/Bridge Switch (page 8). When it is NOT in Stereo Mode the unit only uses the Right Channel controls and input.

http://img3.musiciansfriend.com/dbase/pdf/man/m_480824.pdf

STEREO/PARALLEL/BRIDGE switch
Use this switch to select the operating mode.
• STEREO mode
Channels A and B operate independently (as with a conventional
stereo amplifier). The Channel A input goes to the Channel
A output jacks, and the Channel B input goes to the
Channel B output jacks.
• PARALLEL mode
The Channel A input signal is output through both the Channel
A and Channel B output jacks. The Channel B input jacks do
not function. Channel A and B volumes can be independently
adjusted.
• BRIDGE mode
The Channel A input signal is output from the BRIDGE output
jacks. To adjust the volume, you must use the Channel A volume
control knob.

I have similar problems with inputing stereo sound. How do you know your mic port on the PC is set for stereo? What kind of a cable are you using? If it is an XLR, the connection is pure mono. Maybe you need a TRS cable, which looks like a 1/4 inch jack but is really stereo. Maybe you need a stereo mini. Usually a cable mismatch is the problem. Is your phantom power supply passing stereo? All the ones I have seen are mono. You may need two. Is your sound capture set for stereo? Are the input level controls set correctly for equal volume on left or right channel? I would try the mic with a regular amplifier to insure both channels are working. Then trace the signal from mic to power supply and power supply to computer.

push the monitor button to go mono instead of stereo.