It definitely is HQPlayer upsampling, both DSD downloads, SACD rips, CD rips, FLAC downloads, etc. up to DSD512/48 (24.6Mhz). The Yaggy does not do DSD, therefore it can not play anything upsampled to DSD, so the only comparison would be comparing PCM capabilities of the two DACs. I think the T+A would probably compare very well going by the opinion of a club member who writes for Stereophile. He is a fan of PCM and did not use any DSD512 files in his review of the DAC 8 DSD. He rated it as very good.
I have honestly never listened to anything but DSD512 since getting the T+A. This is the main reason that I believe most people buy the T+A. So to compare the two head to head the T+A would be greatly hampered to its less emphasised section. They use completely different sections, BurrBrown chips for PCM but their own customer 1-bit convertors for DSD. Even so, I believe they would be very close.
I just realized you are probably thinking a PCM file played through the Yaggy and the same file upsampled to DSD and played through the T+A. Probably would depend on if you are a fan of DSD or not. However, in my view, and most T+A owners, I would take DSD over anything playing straight PCM. Not that PCM can't be great, because of course it can. But head to head at their best, Roon->HQPlayer (through a powerful enough computer)->good USB cable->W4S Recovery->same USB cable->T+A... might be interesting.