As you say, Pa7 is already a clean amplifier with low noise, low distortion and flat frequency response, and in the top 20 of all amplifiers tested here. You will not get the "better" sound you are looking for by upgrading the amplifier.I m listening on moderate volume levels, but i m thinking about better sound, like fuller midrange, fuller bass, bigger soundstage etc. I making a mistake? Pa7 sounds good, very clean, that s why i m asking if it s worth upgrading or not
You need to be looking at speakers, subwoofers, room treatment and/or room correction/equalisation.
It would be best to start with investing in a measurement microphone such as the umik1, and just measuring what your system is doing now.