Considering an upgrade

The advantage of your PC is the Roon core. I'm not sure why you would want to replace the PC also, since you are already using Roon. I can understand asking about what might be an upgrade over the BDP-2 and/or Yggdrasil gen2.

The biggest change would come from changing your DAC. The Yggdrasil has a fairly distinctive sound in my opinion, and there are lots of other DAC options out there that might sound better to your ears. On the other hand if you auditioned a bunch of DACs before deciding upon the Yggdrasil, maybe you should just stick with it since you said you're happy with what you've got.

There are Roon Ready network streaming DACs, which would replace both the BDP-2 and Yggdrasil. My personal recommendation in that case would be to look at Lumin, for the hardware and firmware quality. Since you're already using Roon, the software ecosystem of any network streaming DAC would not be a primary concern.

Regarding your question about upgrading from a BDP-2 to a BDP-3, the majority of differences are around the feature set and software capabilities.

Thanks for all the comments. The only reason I was considering replacing the PC as the Roon core was to find something that could work in my stereo rack and eliminate the Ethernet cabling. The current PC is not silent so it's located in another room. I think I'd probably only consider replacing it if I could combine with a streamer. So the W4S or Innuos devices are definitely options too consider. 

My Yggy DAC is now my oldest component. I had a W4S Dac-2 prior to this and was never happy with the sound. I ordered the Yggy based on the positive reviews and liked the way it sounded so kept it after the trial period. So I haven't actually auditioned anything else in my current system. 

I went many years without making significant changes to my system. It's only been the past couple years that I've been working to upgrade my system to get the level of sound quality that I can be happy with for a while. 

I'm not sure that I want to upgrade the digital front end, but since these are now my oldest components, I thought I'd at least explore the options. This is also driven somewhat by my acquisition of new speakers which are much more revealing. 

@jaytor regarding a silent PC you could pick up something fanless like an Intel NUC for relatively low cost, and migrate your Roon Core onto that device. If you really like the Roon software.

I'd recommend checking out the user interface that you'd end up using with any other music management devices, if you're willing to replace the Roon Core. Besides the W4S and Innuos there is Aurender and Lumin (requires an external NAS).

But going with separates for the DAC and network streamer will open more options for a change (improvement) in your sound quality. Auditioning different DACs is what I'd recommend.

Thanks for the comments. I really like the Roon interface and have a lifetime subscription. I also have four Bluesound Node 2is that I use for other zones in my house, so I would like to stick with Roon. 

I've spent some time looking into the Innuos Zen Mk3 and it seems like a good value. For those that have used this as a Roon server and endpoint, does it have enough horsepower to handle a few zones (almost always playing the same music) and a little DSP work (such as a couple of parametric equalization filters)?

I have a couple of old Intel NUCs lying around from my business, so installing Roon ROCK on one of those might also be an option. Anyone have experience with this? 

I'm also interested in hearing about DAC recommendations in the <$6K range that would be noticeably better than the Yggy. Particularly in the smoothness of the midrange. The dealers in my local area don't seem to carry many of the "hot" DACs, so auditioning will probably require a purchase with return option, which I'm somewhat reluctant to do unless I feel there is a good chance that I'd keep it.

The three DACs that I've read a lot about that seem intriguing are the PS Audio DirectStream, the Lapizator Amber 3, and the Denafrips Terminator. 

I’d add the Metrum Pavane Level 3 DAC to your list. It’s also an R2R DAC like the Yggy, but the Pavane is a non-oversampling design that generally tends to sound smoother and more “analog” like, which sounds like it may appeal to you. I believe Hifi Heaven offers a purchase and return option, and it might well be worth considering if you haven’t yet heard a NOS DAC. People who love them, LOVE them.  FWIW, and best of luck.