Rossini Transport ? It is fabulous and I love mine. A huge uplift ( to an unexpected degree) from the Paganini transport that preceded it.
It uses the new(ish) Denon/Marantz SACDM-3 transport mechanism . Better than the otherwise excellent one installed in Rossini Player I would think with, of course, SACD replay to a dCS DAC. Note though, it is HUGE and heavy. The disc tray also takes a moment to get used to as it the disc indentation which holds the CD/SACD is a very tight fit.
I think Rossini DAC should be thought more of as a sister model to Vivaldi rather than a ( big) step up from Bartok. The software is more sophisticated in Rossini and , like Vivaldi, has the ability to be run faster ( see the choice of Mapping ) which offers a huge improvement ( ask any of us who upgraded Vivaldi to Vivaldi 2) and is not available with Bartok.
Yes, your future plan to use it with a later upgrade to Rossini DAC or even Vivaldi/Vivaldi replacement makes sense.
If the ex-dem model is in good condition ( and hasn’t been run 24/7 to provide background music in the shop 
) and the price is right then do it. I am mentioning the amount of shop use because optical pickup units are consumables ( hopefully long term though).
Remember to get a clock cable so you can slave it to Bartok set to Master Mode.