I own M50s and M80s. I expect you've read my comparison threads between the M22s and M50s, and between M3s, M50s, and M80s. M50s are very nice speakers; but they're outdone by the M80s, and in some circumstances by M22s and M3s. As I recall, the added body (bass, presence, whatever you want to call it) was good for certain types of music, but lost out on others.
I have not heard the EP350, and I don't have an EP500, but from what I've read, the EP500 is the same kind of leap above the EP350 as the M80s are above the M50s. Given your choices, I would probably go with M22s and the EP500, assuming I could get over my bias towards tower speakers.
