Look into the new ports forum, and the wiki.
I think this brand of players has been discussed before...
Okok, I find info on forum and did update the wiki about this
http://www.rockbox.org/twiki/bin/view/Main/OtherTargets
S1MP3 based playersLots of documentation on the players can be found at S1mp3.org.
The problem with S1MP3 players is that there are literally hundred of variations of them sold under different brands (this is why SO many different manufacturer`s firmwares). Their main internals are usually very similar, but some of them have completely different DSP chips, FM tuners, or screens. This means that it would be impossible to have ports for every variation.