How do I gain control of my JBL marine radio

I contacted JBL, and Pioneer about the RCA outputs of the DEH-P5800MP. I got a question answered by JBL that you should gain your amplifier, or amplifiers at half of the Head Units volume, in which case the 5800 model has a max volume of 62. I would assume that this goes for any unit since I didn't give JBL the model or brand, which indicates that they are giving a tip on every, or most units unless specified. You can e-mail the manufacture on what unit you have just in case yours is different. I found after a good conversation with the technical support guy at Pioneer that you should turn your volume up to 25-30 (25 for your loudest CD, and gain it from there. I told him that I was an audiophile and he suggested that I could gain it at 45 for my lowest recorded CD. I have been installing and gaining systems at 3/4 volume, or if the max volume was 62 then I would gain my lowest recorded digital CD at that volume. I was amazed that JBL had an answer for probably 90% of the head units, and I have learned something new. I was under the assumption that the higher the volume the more voltage the RCA's put out allowing you to be able to have your amp gain at a lower level. From my experience of 12 years, hearing both companies say roughly the same thing it is apparent that Pioneer units with a 2 volt output should be gained at the 25-30 volume range(probably for your lowest recorded CD. I have CD's that are pure digital and bass CD's and CD's that are recorded louder (like techno music, or alternative music) If you know what you are doing, and can hear distortion, like I can, the tech said that I could gain it at 45 for the lowest recorded CD. This allows your lowest recorded CD to be played at max volume at 30-45, and your loudest CD's would be at peak volume before 30, or 45 if you choose that route. Keep in mind that less power blows speakers before more power does. That is the best advice I can give, and I will adjust my system accordingly to there recommendations. Thank you