Amp Head to Pair with Markbass NY112 ??

Have you tried a Markbass head with the cab? The older, class AB LM IIs and LM IIIs have a nice, warm sound relative to some SS amps (warmer, I'd say, than the MB200, though flatter in voicing with knobs at noon) and mate well with that cab. The newer, class D versions of the heads should be pretty close and the LM250 might be good as well.

A first-gen Euphonic Audio Doubler is another clean-and-clear-but-not-sterile sounding amp (and, as its name suggests, nice for doubling). They turn up used now and then for reasonable prices.

The Genzler Magellan 350 and the Mesa Walkabout are two more voiced, warmer-but-still-capable-of-clarity options I could see working well, given your modest volume needs.

That said, I might be tempted to try a different cab -- I have an older, Italian-made CMD 121P combo that I recently had repaired (amp was fried), which had sat on the sidelines for several years while I played other gear. The head sounds great through my other cabs but I don't like the combo-cab (not exactly the same thing as an NY 121, but not too far off) near as much as I remember. That said, I've only played the thing at home since getting it repaired -- I remember it being a potent little bugger live with a group, and that's the real test. (I plan to pick up a pair of MAS 18s in the next few months for electric and perhaps some upright and amplified cello -- will see how they do!)

You might find your HX-Stomp explorations instructive, too -- I don't know how well running into the MB200's Aux-in would work but, if you want to use it as a more-or-less neutral poweramp, you can approximate a flat response with it by running into the front end and cutting bass and treble and boosting mids slightly (I don't recall the exact settings -- been awhile since I had mine).

Let us know what you do and how things go!

 

MarkBass NANO 300. Lovely little amp.