Which would you buy: dCS Rossini non-Apex or dCS Bartok Apex?

I have the DCS bartok and I think the Apex upgrade was a big step forward. Everybody hears differently, but I disagree that it is not musical. In fact, I find it to be a more realistic sound, than audio research equipment, which, to my ears, puts a veil over the music. I think both are extremely well designed and well built equipment, we all have different tastes.

The ideal situation would be to get the Rossini and upgrade it to the Apex. If that’s not possible, I would probably take the Rossini, but as I said, I thought the Apex upgrade was a very significant step forward for both Rossini and Bartók. 

Give the Mola Mola Tambaqui a listen if you can. 

Before you purchase give Nagra Dac’s and MSB a shot. You can get an MSB Reference Dac with warranty from MSB at a great price. While DCS comes highly recommended there are other sound signatures you may be over looking in that price range. 

Good thought to get a general directional idea of how each DAC sounds.

I’ve not heard either but I can tell you that I’ve gone thru 5 DACs in about a year and the conclusion I came to is you really have to spend at a minimum a week or two with a new DAC in your system to get a feel for it. 
If you tuned your system and room and it sounds good, swapping a DAC might change that balance and you end up not hearing the full potential of the new DAC with a quick A/B. Similar to upgrading an amplifier or a preamp, a new component is almost never plug and play. It may trigger additional changes that include speaker placement, cables, acoustic treatment, etc. This is in addition to your ears needing to adjust to new sound. 

Audition before buying especially when you’re about to drop this kind of penny. Or buy with return policy. 
 

Sheet. I'd buy a Playback Designs MPD-8 100 times out of 100 before a DCS.