dac and streamer or seperates

If you have an onboard dac with the Krell, maybe you would want to start with the streaming transport and wait on the dac.  You may like what you have!

As an fyi, as a Lumin dealer, I'm a fan of the U2 Mini!

At your budget, definitely separates.  A Gustard R26 DAC and the new Innuos Pulse streamer would be in your budget and be a great combo.  With a streamer you want to pay attention to its software/app, and by all accounts the Innuos Sense app is a winner whereas some other streamer’s apps get some mixed reviews.  Best of luck. 

It looks like you have a pretty good dac, at least based on the chip that’s used.  I realize implementation matters, too.  I think separates is the way to go.  Many more options for pairings.  I have an integrated with onboard dac which is pretty good.  I bought a HiFiRose 250a, which is an all in one solution that has the same chip as your Krell I believe, that I had for about a month which was big step forward. I replaced that with Denafrips Pontus II 12th using a MacBook Pro as the source running Tidal and Qobuz that sounds better than the dac in my integrated amp and the HiFiRose.  Denafrips, Gustard or Holo Audio with Innuos, Aurender, Lumin or Auralic would certainly be around your price range.  The dacs I mentioned are R2R dacs which likely have a more analog sound than the delta-sigma dac in your Krell.  I know my source is the weak point but I really like the interface for Tidal/Qobuz via the Mac and since it still sounds better than what I had upgrading to a dedicated streamer can wait a bit.  Sorry, that was a lot, some of which may not be relevant.  Logorrhea.

All the ’high end’ (apparently!) "streamers" are essentially SBC PCs. If you educate yourself on how to build a "audio optimized" PC, you will have all the freedom in the world wrt choice of hardware and software optimization. But, if you buy a ’high end’ (apparently!) streamer, i.e., have some other dude do some work for you and put a brand name on it, you will just fatten his wallet and be locked into any crap he gave you.

If you have hires files that you just plan to stream from a nas, or tidal/qobuz. forget about a streamer and get a streaming enabled high quality DAC such as the Gustard R26 --> use with bubbleupnp on any android device. You could have some jaw dropping sound quality at this kind of price...

I would recommend Aurender NH150 and Schiit Yggdrasil. Works well for me!