Would I need a mixer or amplifier with this product: Pyle-Pro Rack Mount 8 Channel Wireless Microphone System with 8 Lavalier/Headsets (PDWM8900)

This model does not have the facility for extra microphones. However, for $99.00 USD you can purchase a two mic lavalier system. It might be easier, cheaper and less frustrating. Keep in mind, I am not an employee or in any way associated with the store that I am sending you a link to.
http://www.musiciansfriend.com/search?typeAheadSuggestion=true&typeAheadRedirect=true&sB=r&Ntt=+2+Channel+UHF+Microphone+

http://www.peavey.com/products/index.cfm/item/699/116338/PV%26nbsp%3B20%26nbsp%3BUSB

Look under "Downloads" tab at bottom for owners manual info. In a nutshell...mic to mixer channel #1, mixer connected to power amplifier, amplifier connected to speakers. Start with zero volumes on all equipment, bring up amps 1st (1/2 volume) and then adjust mixer until sound is heard from the microphone.

Instructions

1. • 1

     Place your mixer in a location that will allow you to hear the sound coming from the speakers clearly. The best placement is opposite the speakers, centered between the left and right pair. Connect the power supply to your mixer.
     

   • 2

     Connect the female end of an XLR cable to a microphone. Run the other end of the cable to your mixing board. Plug the male end into the "Mic" port of an open channel. These channels provide the preamps that will shape the sound characteristics of the microphone signal, processing them for output. Repeat the process for each microphone in your rig
     

     
     

   • 3

     Connect one end of a balanced 1/4-inch cable to the left channel jack labeled "L" found on the "Main Out" panel. Connect another cable to the right channel jack with the "R" label. Connect the opposite end of each cable to the matching left and right inputs on you amplifier.
     

   • 4

     Power on your mixer and amplifier. Test each microphone connected to the mixer for output.
     

   • 5

     Adjust the volume of each microphone channel to create a balanced mix. Use the "EQ" knobs to shape the tone and cut out frequencies that are causing squeal and feedback.
     

   
   Audi Performance Chip
   

Effects plug into mixer, mixer plugs into power amp. Others may want the mixer and the effects plugged into the power amp for the most available inputs. (when multiple inputs are available.)

Effects and mixer are a line level output and the mixer can be considered a line level input as well. A mic mixer has gain amplifiers for the inputs that are below line level such as unamplied microphones. It is possible to parse to absurdity, but the gist of it is above assuming you do not want to apply the same effects to everything all at once.

Isolate one channel at a time to see if a particular channel is the problem. Make sure ALL interconnected equipment is powered from the SAME receptacle or power conditioner. A remote amplifier MUST be powered from the same source as the mixer, even if it requires a separate run to power it. Make sure all cables are BALANCED, either XLR or TRS cables. Sometimes a cable can have a broken wire or shield and cause this.

Find if there is reverb. Not sure where you are putting the IPOD into the unit. Turn off the effects for that channel. There is usually a control for each channel that controls the amount of the channel sent to effects in addition to the normal mix gain. It sounds like yours got turned up for the IPOD channel.

I suspect that one element of the crossfader pot (slider) is broken. Possible cause is if something fell on the knob or wear from use.
If one end breaks on one channel, the opposite end side will remain on full while the other channel will behave normally.
Replacement of the dual pot will LIKELY involve removing all panel knobs to remove the circuit board to replace the pot after disassembly of the unit. Not for the casual DIY person.

Here is a link to the manual:http://www.peavey.com/assets/literature/manuals/00513220_7.pdf I didn't look at the manual for the crossover but this is probably the way I would do it. Look at page 13 in the manual : Come out of the Main out (31 in the diagram) into the main in of your crossover. Go out of your crossover Hi and Mid out setting back into Power amp In 1 (labelled 32 in the diagram). Hook your speakers that you normally use to the output jacks on the back of the Peavey. Make sure you match the output impedances. Go out of your crossover low output into the Pyle power amp and out of the Pyle into your subs. Make sure the impedance ratings of all your speakers match the output impedances of your amps. You will only be running in Mono mode as that is the signal output of the Peavey mixer. You can run faux stereo by using the Main monitor Out as 1/2 the pair and the Main Out as the other 1/2 to both channels of the crossover but you won't be getting a true stereo pan mode.

Troubleshooting is always a "process of elimination." Have you tried hooking up your Peavey powered mixer to another set of speakers? How about connecting the speakers to another audio system? Your term "very little sound" could mean audio input problems, mixer/amp settings or failure and possibly speaker damage (internal passive crossovers). Please be more specific.

Here is a link to what your looking for,
http://pro-audio.musiciansfriend.com/product/Yamaha-CM500-Headset-with-BuiltIn-Microphone?sku=245012

I can't tell from the add but hopefully it comes with adapters for both plugs that will work on your mixer. It does have the one for the headphones but the one for the mic is not clear, they are not interchangeable.

You would obviously plug the headphones into the headphone jack. The knob labeled "Phones/Control Room" will control the volume without changing what's being broadcast. What you hear in you phones is exactly what you are broadcasting.

The microphone needs to go into either mono channel 1 or 2. The adapter for it needs to be a mono Tip/Sleeve adapter as the more common stereo Tip/Ring/Sleeve adapter may cause some problems. You can tell the difference by looking at how many sections are on the plug divided by a little black line. Two sections is mono, three is stereo.

Adjust you microphone level by setting the volume knob, the one on the very bottom, to the 12 o'clock position. Then turn the gain knob, the smaller plastic one on the very top, until the desired volume is reached. If you experience any clipping or distortion turn the gain knob down until it goes away. These are general settings, you may want to experiment until you get the best level without noise.