There are differences in audio low pass filters between different Amiga models. It can't be ever entirely disabled. I think Amiga 1200 filter affects the sound the least.
IIRC, AGA chipset (Amiga 1200, 4000) is also capable of up to ~56 kHz sample rate.
IIRC (that was a long time ago) I could use only 8 tracks on my A600 because I only had a meg of memory. A friend had extended his A600 memory to 2MB and I think he could get 6 tracks.
Edit: Realised that Facebook search is rubbish, this is the actual group URL: https://www.facebook.com/groups/CommodoreAmiga/