Depends on what your feeling are towards to HD800.
If you like then but feel they have faults ( the most common ones are lacking bass, bright or thin sounding) then a tube amp that will help in those areas would be my recommendation.
If you don't hear the faults mentioned above and want to keep the stengths of the HD800 of great speed, detail and bass control (amonst others) then SS would work well.
The HD800's require and need a good amp but that does not have to mean expensive.
All IMO of course.