Using your Bartók at unity gain 0.0dB (so no variable pregain) at 6V out into a good preamp, which matches your Audia amp, and can handle 6V in, is worth trying.
The preamp I am currently using is irrelevant, so far as it is not per se matching your amp, but it anyway is serving me very well. People get upset here when I mention it (again), so PM me if you want to know 
Anyway, my current setup is here: How do you partner your Bartok?
But it will change soon.