After looking at Atmel ARM powered MCUs (AT91 series) and reading some webpages i founded a software based decoder will have this benefits :
-lower consumption
*-glich and bug free mp3 decoding & encoding
-latest algorithms and easy upgrade (OGG Vorbis)
-flex programming in c (i personaly always prefer asm !)
-lower price

(* i don't know much about SND1C but i heared other hardware decoders like sta013 have some glitch problems)

Anyway i really like the C51SND for having this much of abilities just in a single chip along with MCS51 core.

considering the price (in my country about $20) ,maybe i burn some chips till i reach the stable and final firmware for the player i wish !, it will cost me much and i can't afford it right now. so a builded and tested project will help me out to get some spots and keep the cost down.

Best Regrads :
Farshid J.H.
(Sorry for my bad english)