I've definitely been enjoying my RS1i. Wish I could have auditioned both. As it was, I bought (albeit at a great deal) sight unheard as it were.
I guess ps 500 would be much bigger contrast. One thought would be do you want two different sound signatures? Or, would you want to basically upgrade the 225 and possibly sell the 225? I'm keeping both for the moment. I've got two amps now-LD1+ and Asgard-2. I'm going to run one from a dedicated CD based stereo rig w/ Sonos and the other for computer audio.
But, first I need to get an separate dedicated DAC that can accommodate. Right now, I'm utilizing the DAC that is built into an integrated amp that has digital and traditional inputs.
My next move-it will be my spendiest one yet-will be to get a nice CD transport and DAC combo-both separate components from Musical Fidelity. Kind of a MF stack as it were. That will give me a fairly high end CD player and allow me to use the DAC for CD's and computer audio. I have a stereo and computer in the same room. Then, I'll have two little HP rigs up for both applications.
At least that's my current game plan....always subject to change.....
That is my long winded rationale for keeping two headphones that basically have the same sound signature with different levels of refinement