Pioneer DEH-5750 & DEH-3550 Difference

[Gdspd08]

Hi,wanna know is there any sound quality different between these two set of Pioneer HU? I know that from spec, DEH-5750 and DEH-7750 is the same except for the OLED display. Currently my setup is Pioneer 3550 with 2 Twisters amps (500W and 400W) with Accoustic pre-amp, 1 x 10' subwoofer in a box, 1 set of rear component Twister speaker with cross-over and 1 set of front Rainbow component speaker with cross-over too. The sound is loud and good ( I did soundproof) but the clarity seem like not there. My HU is already 1.5 years liao and it is the first few generation of mp3 HU. Only have pre-set mode (SuperBass, Powerful and etc, and 1 custom setting)