What headphone amp to use with Sennheiser HD800?

I use Sennheisers own amp the HDVD 800 which I find extremely versatile in that it is not just a headphone amp but also a complete pre amp with spdif in - Bal in - Bal out - RCA in- RCA out - USB in - AES in . It also has a pretty serviceable DAC in it. The thing I like about it though is it a fully ballanced unit and if you treat your headphones to Sennheisers fully ballanced lead it will lift them to a whole new level ( I mean major improvement ). I find the unit so good I even put my Gryphon Mikado through it and the wealth of detail it produces is incredible. It is expensive but I find it to be very accurate.

I used to have a Bryston BHA-1, connected to my previous McIntosh C50 preamp (not enough "umph" from its built in preamp) with the balanced connectors.  I don't use headphones very often, so I sold the Bryston to someone who really enjoys it.
When Tidal started streaming MQA, I purchased a Mytek Brooklyn DAC and the headphone amp in that baby has a LOT of power!  So, it's become my headphone amp of choice, powering my HC800's.

I use an Ayre Codex DAC/amp in balanced mode with a pair of Sennhesier HD650 and they sound great.  Works well as a standalone DAC. 

I have had Burson Soloist w/ the warmer of the 2 dacs offered.
I found it a bit bright w/ LCD-X

Used the McIntosh MHA100, and it was great, but more expensive
than I felt was a great value, so I sold it and broke even.

I now use the Bryston BHA1 with a Bryston BDA2 and it is a great great match for the LCD-Xs and I'm sure would be also for the Sennheisers...
I've heard good things about the Ayre Codex.
If you don't need a built in DAC, you might look at Wells Audio's headphone amps......have heard them at RMAF and they are probably the ones to beat overall in my opinion.........if you go tubes, I'd go Decware Taboo