Well, I've started sound dumping some music for this game, through Gens+. Currently the music is as follows:
Green Hill: Door into Summer. I forget which ripped I used... a Chaotix rip, or a rip from Sonic3K Megamix
Hidden Palace: I dumped the music from Dark Fortress Act 3 in Sonic 1 Megamix. I can't place my finger on the music's original game, and I'd like to get the original music.
Sol Sanctum*: Sol Sanctum music from Golden Sun. It's too good to pass up. In fact, that's where I got the name. =P
Carnie City: Spring Stadium 1. It sounds pretty good already, the only slight problem is the beginning on the lower quality. It's barely noticible to those who aren't 'trained' in music stuffs.
All of the music is in MP3 format, and doesn't interfere with the frame rate. Probably cause I cut down on the quality of the sound, down to 64 Kbits, or whatever. The difference is a bit difficult to spot, but it cuts the file size by 3/4, a grace for me. =P
* Sol Sanctum is the resting place of the sol emeralds in this fan game, if anyone's wondering. Yes, I do plan on incorporating some Rush story elements into this. However, never playing rush has put a damper on my knowledge of the story line.
Well, I'll upload a few updated screens here.

The basics to Green Hill Zone. Those who followed my hack will recognize the art. The trees from my now scrapped South Island Zone, and the general GHZ theme.

Showing the top of a loop and Super Sonic again. I don't have the full loop cause it's just "floating" there, with no art connecting it to the rest of the level.