Tube Pre with Benchmark AHB2 Amp - anyone doing this?

Could be. Regardless, the devil is in the details. If using a SS amp with tube pre-amp, imdepance matching is key to getting best results.   If you go with a SS amp that has at least 50-60kohm input impedance, one would expect good results.  We’re it me I would look for 100kohm input impedance minimum to be safe. 

@invalid , true, Not all.
Linear Tube Audio for example. That’s due to their proprietary ZOTL technology that makes them unique. Good stuff. Quality more-SS like sound but with tubes. Something different. The “linear” in the name is appropriate.

Tube preamp is a good way to go if low distortion SS sound is not your thing.

I moved from tube preamp to SS Freya personally.

Tube preamps have higher output impedance. That can lead to much of the resulting sound being softer, less dynamic, and “easier on the ear”, but for best performance in those areas, you want a SS amp with corresponding high input impedance. So different amps will likely sound more different with a tube preamp. Impedance matching matters more than ever with a tube preamp.

AHB2 input impedance specs look decent for use with a tube preamp, but I can  assure you Benchmark products in general are not designed with tube pre-amps as a primary consideration.