Personally I think you may want to try some better interconnects (not knowing what you may be using). I just switched to some Nordost Frey ic's got a much nicer soundstage and imaging. Definitely more air between the instruments and vocals. I also found the same when I switched to Frey speaker cables a couple of years ago.
The Supernait was my first affordable choice when I upgraded my Bryston B100 but I did go the 'dark side'. I ended up with an Octave V70se with a black box (comparable to the HiCap with Naim) with KT88 - 6550 and EL34 output tubes. The HiCap is a great suggestion for your Supernait. Tube rolling for me is a ton of fun. The El34's have all what you seem to be looking for in sound which is what I'm currently listening to. I do also use a Rel B3 sub and would say I'm in heaven. Note I have never heard the Harbeth lineup but I do have the Dynaudio C1's.
The Supernait was my first affordable choice when I upgraded my Bryston B100 but I did go the 'dark side'. I ended up with an Octave V70se with a black box (comparable to the HiCap with Naim) with KT88 - 6550 and EL34 output tubes. The HiCap is a great suggestion for your Supernait. Tube rolling for me is a ton of fun. The El34's have all what you seem to be looking for in sound which is what I'm currently listening to. I do also use a Rel B3 sub and would say I'm in heaven. Note I have never heard the Harbeth lineup but I do have the Dynaudio C1's.