I own a WiiM Ultra in a third system but have quite a bit of experience with it now. I I use it as a streamer only as the DAC is not that good, imo. So upgrading the DAC for $500 might be a worthwhile upgrade.
Alternatively I think the EverSolo DMP-A6 could upgrade both - but if you can swing it I'd sell the WiiM and get an EverSolo DMP-A8 as it is both an excellent streamer (much better than WiiM) and an excellent DAC for the money. I run my DMP-A8 through a McIntosh 352 and it has a great sound that is getting close to my primary system that is McIntosh C49 preamp whose DAC is great for me. So the Eversolo streamer is great, the DMP-A6 DAC is okay, but the DMP-A8 has both a great streamer and a very good DAC - I think FOR THE MONEY this is best I've heard lately.