I have something very similar on my desk at work. SMSL SU-8 into Loxjie P20 powering either HD6XX (balanced) or Beyer Custom Studio (haven’t gotten around to rewiring these to balanced yet).
It sounds fine to me 
There is also a thread on the P20 that has plenty of opinions and useful info here: Loxjie P20 Balanced 6N3 Tube Hybrid Amp for under $100