I have tried Audirvana 3+ yesterday. It's incredible how smooth the experience is. The UI looks tons better than JRiver's and browsing album art feels like 120 Hz opposed to 12 Hz on MC23. When using the latter I feel like I am running Windows software through Wine emulator on Linux...
But unfortunately Audirvana is not even close to Media Center's feature list because it thinks bad about DSP: no (parametric) EQ, no crossfeed, no convolution, not even listening tests, ... basically nothing that let's you experiment with audio and I think that is also an important part of audiophile listening. Whole bunch of marketing for a ridiculous price. Shame.
I also came across the open-source Kodi but it was not what I think it would be. So I continued my search and I couldn't find any software that comes close to MC, unfortunately.
Before making your final judgement you really should check under Help > System Info... to check if all thumbnails have been built, and if any background processes are still running, since this is a new installation.
Thumbnails built: 100%
Audio analyzed: 100%
Background tools running: No tools currently running.
It's nice to hear that JRiver is still working on improvements. But let's be honest here, MC23 has zero new features over MC22, or am I missing something? An internet radio channel called Kiss - that's what JRiver charges 27$ for? So when the Mac improvements hit, I will be paying 50 $ for what looks like a beta program and a year later I can pay another 27 $ without new features just because JRiver thinks they need to charge users every year. What if MC24 has zero new features (a new radio called Queen) but MC25 brings the Mac improvements. I can't upgrade from MC23 so I have to pay a 2x 50 $ or 50 +27 +27 to stay up to date... They could just as well start a subscription plan for 5 $/month. But even then we wouldn't even know if they ever fix the Win98'esque UI.
Sorry for the rant. I was hoping there would be an easy fix to my problem or box I forgot to tick for hardware acceleration or something. I didn't expect to have to live with the lag.