Upgrading digital side

I've heard the Bricasti M21 and it's amazing, very neutral but the most important thing I heard is it's musicality. If you go this route look no further than their newish M19 transport. What makes this combo special is their IS2 connection.  (I'm envious already).

Really depends on what specific improvements you’re looking for and what sound characteristics are most important to you, especially for the DAC so I’d suggest sharing what specially you’re looking for to get more helpful/meaningful recommendations here.  With a really good streamer with storage you may find your CD transport being very rarely used, so I’d keep the Jay’s at least initially until you see how that works out.  By most accounts Innuos’ Sense app gets the highest marks for usability to the point that some Roon users ditched it once they had Sense, and I’ve not heard that said about any other streaming app so may be something to consider on the streamer side.  One thing I’d budget for is also upgrading the entire digital chain including the switch, Ethernet cables, etc. as those ancillary pieces can be critical in matching and possibly surpassing the sound quality of a really good CD transport.  Like everything in audio the chain is only as strong as the weakest link and everything matters, and that definitely holds for the digital chain.  Just some thoughts FWIW, and best of luck. 

I would also consider Antipodes on the server/player side, they offer a lot of flexibility in terms of software options, and their hardware and support is excellent. Worth a look.

• Server
• Streamer/endpoint
• DAC

How you stream music makes a difference but, in general, my experience is that your money should go in the opposite order of the list above, with most going to the DAC to achieve the biggest bang for your sonic buck.

As you pointed out, the Grimm MU2 does it all, and very well based on most reports.  You could also consider something like Meitner’s MA3i, which serves as a streamer, DAC, and even a volume control, but you would still need a server to run Roon core and store your files.  At reasonable prices, I have had good luck with Small Green Computer servers, especially when paired with a good streamer, like Sonore’s top model or something like the Innuos Pulsar. Separates work well, and particularly for flexibility but, at your price point and considering your needs, you might find that the Grimm delivers it all. As pointed out by @soix, you could rip your CDs to the server and then sell the Jay’ to increase your budget for the new stuff.  Ripping to a SGC server is a piece of cake.  I still occasionally buy and rip CDs even though I have nothing to directly play them on.