Thanks so much! Yes, I'm starting to lean towards just keeping this unit until it stops working. It's not so much that I feel a strong urge to "upgrade"; it's more that I want to see if there's a way to at least get close to where I am now in terms of performance with newer components--at an affordable cost.I'd echo the suggestions to stick with your current setup unless you think it's broken or particularly flawed (doesn't sound like it). Your dual input option is particularly handy and difficult to replicate without buying 2 new amps.
Fix it if it breaks?
That itch to upgrade is a beast Plenty of other ways to spend the money ... including measuring your current setup and looking at EQ or room treatments.
(I also have the Zen Phono btw, and like it, but there's no way of knowing how it compares to your existing kit which may be just fine. There are other good options too)