I, like you, looked at the pics and decided that they had exactly the same circuit, the odd component was different, but that just might be new stock. So bought the 5.3 and psx second hand ( for the price of the 310 alone). It is hard to believe that the 310 is better sounding. The 5.3rs is just spectacular, and i think would be hard to beat without spending 10 to 20 times the price. I could not fault it, and there is nothing I am missing that makes me want to try something else, except a second input:) Can't say I have tried it without the optional power supply though.