dcs bartok vs DENAFRIPS TERMINATOR-PLUS

You didn’t mention what you have today? The dCS and Denafrips are going to sound a bit different. The dCS is going to be a bit more more forward and detailed.

Alternative options would be the Chord Dave with an MScaler which I think beats the Bartok and is in the same league as the Rossini.  dCS and Chord have a similar approach (FPGA) and similar sound profile.  

For the more natural, slightly less forward sound of an R2R DAC, I would look at Rockna. The Wavedream Signature can go toe-to-toe with the MSB Premier in terms of sound quality.  It is a brilliant DAC.  Although not made in the UK, it is made in eastern Europe (Romania) rather than in China.  

That amp and those speakers look amazing. Which DAC is best is going to depend on the exact tonal profile of the piegas. Assuming that is a typical ribbon (and is nor terribly bright) my hunch is the Dave and MScaler combo would be the slightly better choice. That being said, I also assume that the amp is not fully balanced. The single ended version of the Rockna Wavedream Signature lists for $11K and may be just as good for less money.

You could add the Rockna Wavedream (with Rockna) server or a K30 from Antipodes (with the Dave) and have and insanely good digital system that will give you every drop of clarity available from your new amp and speakers.

I am not running ribbons here at the moment but am running Art Audio Opus 4s which little KT88 based monos.  You and I might have similar taste.

Good luck!