Forgive me if this has been covered in another post (I did look), but are there any advantages to having a matched pair of 12AX7 tubes in the ZP3? I am thinking of getting a Mullard 10M pair and want to know if I should pay extra for matching. Thank you for any advice or insight.

Glad you found the answer. I've tried matched sets as my previous phono pre used a single 12ax7 per channel so I had a few sets. By all means you can use a matched set, but the infinite possibilities of different tubes can really help with fine tuning. Downside of that is where to start with so many possibilities.  I've swapped so many tubes the ZP3 it's hard to remember them all. What I found is that I like the "quiet" versions of the 12ax7 like 12AX7A, 12AX7LPS, or 7025's in the input (closest to front) slot.