The only difference is that the 550 has analog outputs (which isnt a problem since you are using HDMI) and the 550 can decode DTS-MA internally while the 350 transfers it to LPCM. If your reciever is HDMI 1.1 compliant you should be able to bitstream via HDMI all lossless audio signals (please double check this on me though, am foggy if it's 1.1 or 1.3 compliant, but pretty sure all you need is 1.1 I have the 350 hooked up to my Denon 3808ci and am bitstreaming everything and letting the Denon do all the decoding and I get all the lossless audio (even though the 350 cannot cannot decode DTS-MA)
