"04-17-15: Onhwy61
If you really want to alter the frequency curve, then use an parametric equalizer.
Onhwy61 (System | Threads | Answers | This Thread)"
Generally, I would prefer a different solution, but in your case, it may be the best way to go. Fooling with cables is no way to go about it. Something like a Behringer 24/96 digital eq should give you some good results. Since its digital, you can run it through a DAC for better SQ. The only other thing I can think of, besides an eq is to get a more powerful amp. The amps you list as tried are not the last word in power and control.
If you really want to alter the frequency curve, then use an parametric equalizer.
Onhwy61 (System | Threads | Answers | This Thread)"
Generally, I would prefer a different solution, but in your case, it may be the best way to go. Fooling with cables is no way to go about it. Something like a Behringer 24/96 digital eq should give you some good results. Since its digital, you can run it through a DAC for better SQ. The only other thing I can think of, besides an eq is to get a more powerful amp. The amps you list as tried are not the last word in power and control.