i upgraded from c3 to s350 last year when my c3 subwoofer out KO.

things i like about c3:
1) separate amp
2) speaker cable for the connection
3) smaller satellite foot print
4) easy access line in and headphone out
5) vol level display

things i like about s350:
1) better build quality.. looks more like solid wood than mdf finishing compare to c3
2) sounds better.. big improvement over bass (punchy and tight compare to c3)
3) having Bluetooth connection (not sure if c3x has bluetooth but c3 dont)

no regret for the upgrade but still not satisfying to my liking

if your area to cover is not too big S350 or S360 will be good enough to do the job. Audio clarify and low bass improved over C3x. If you are using bluetooth and u r going to change it to optical/Rca certainly it will be a big improvement