The problem is the output voltage from the MP3 player is very low so it is taking alot of gain from the 3803's amp to get it up to the levels you want. The only other way I can think of would be to try using a headphone amp inline with the MP3 and 3803 to boost the input voltage into the 3803; but I wouldn't worry about hurting the 3803 right now, if the music still sounds good with just the MP3 feeding it, just keep doing it, you won't hurt anything.


Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70