From Rossini Apex to ????

I think that, ultimately, the choice is in the ears of the listener. However, the Bricasti M21 DAC is within the same price range (at $16K MSRP) as the two excellent DACs you have identified; it also is a splendid DAC.

I recently listened extensively to both the Mola Mola Tambaqui and the Grimm MU-2. To my ears, the MU-2 was not only the better of the two, it was spectacular. The only DAC I have found sonically competitive to it was the Bricasti M21 (which I recently purchased). In my case, price was a factor. I was able to get a good price for the M21, whereas the MU-2 is significantly back-ordered, making your obtaining a discounted price for one unlikely. 

The Linn Organik DAC is worth auditioning. To my ears, it sounds sweeter than did the dCS Rossini because it does truly have an organic, visceral sound that is at least as detailed as the dCS Rossini.

Try MSB.

I got a used dCS Rossini + clock combo. In my system it was a great upgrade from Tambaqui. Sound is very balanced, detailed and enjoyable. Clock makes it very precise that results in impeccable vocal quality. Overall I feel dCS makes great products that deliver value (specially used market) 

Consider the playback designs mpd8

I used to own the Tambaqui and the MU1 (lost interest in the MU2)

Below is a Rossini apex owner opinion (I know a couple others who came to same conclusion…)

https://youtu.be/-64u03HryVw?si=9phTSoU_vRBPxLla