Based on this information
http://www.rockbox.org/wiki/PhilipsGoGear which I gathered, a port seems unlikely because:
- Generation 1 (G1): don't know which chip is inside, must be STMP, but one would need to get one to check
- G2/G3: if confirmed STMP37700, will be hard to port (not impossible but hard)
- G4: if confirmed Actions, one would need to buy one and disassemble it to find out which chip it is
So at this point, we lack a lot of information, someone with an actual device and willing to disassemble it and taking some pictures could help clarify the situation. You can find your device's generation using the above mentionned wiki page and the model number (SA2RGA for G2 for example).