Actually understand how you feel. At work a catchy tune sometimes goes through my head and end up forgetting by the time returning home which is kinda disappointing. Happened so many times, occasionally when trying to sleep too. Some of the packs I purchased are 16bit 44.1khz stereo but none are 24-bit. Honestly 8-bit has too much noise (amplitude too low?) but here is what I mean. In a SNES cover of a DS song I try to use gamecube instruments. The string sample (multisample instrument, Pokemon Strings which come from the Halion String Library) is 1.01 MB. 16-bit mono at 44.1khz C5. Compressed to 8khz at C5 consuming 18kb, it does lack a bit of clarity but for a SNES the quality is pretty remarkable.
Perhaps the issue is I don't know what type of music you compose. During middle school I did a lot of orchestral stuff (even if it sounded terrible) and as a result rarely making use of nifty effects, thus the realism often came from the quality of the instruments and touches of reverb to simulate an auditorium. Sadly I can only think you might give MilkyTracker one last chance. I don't make SPCs directly but rather convert them (.it file) via SNESMOD.
Here are some SPCs. Whether it be the echo buffer (often for expanded sound stage) or s9x (rear) the majority of these make use of the SNES surround sound so having that disabled will affect the audio.