yes what do you say it's true. The character of the speaker always remains, but small differences can be heard with different amplifier.
Agreed,sonic differences do exist between amplifiers.
As far as the AMC not costing enough i would not worry about that,there are hifi botiques charging premium prices for the same AMC amp your looking at,the only way to know which amp is really going to sound better in your home is to try them both in your system.
I have to ask what amp are you running right now & why you feel its not doing a good job? What are you lacking in your sound?
I also have to ask about your vincent,when your running your current set up are you using the tone controls on the vincent or you leaving them in the off or neutral position? The reason i ask this is that alot of guys bypass using their tone controls in order to keep the signal path pure which in most cases is a huge mistake.
A twist or two from your tone controls will offer way more system flexibility over running different amplifiers,tone controls are not a bad thing.
I have not seen your speakers being that they are DIY but from your description of the fostex horn loaded design i'd think speaker placement would be a huge issue in your system.If it were me before i bought any other amplifier i'd experiment heavily with speaker placement & tailoring the sound with the tone controls.
You may have issues stemming from the DIY single driver fostex design that your using that cant be overcome no matter what electronics they are paired with.
