I also have a T+A DAC/streamer and agree the G2 app is limiting and disappointing relative to others I have used.
My personal experience with Roon is a few years old but wasn’t particularly good. I haven’t tried it with my SD 3100 HV units but am disinclined to try again as it quite negatively impacted the sound quality even without using any processing. It’s possible it sounds fine w/ the T+A unit, but I have reason to suspect it wouldn’t be as good as the built in streaming client.
In any case, I personally have decided to live with the G2 application as it’s responsive, stable, and doesn’t require me to install an update every time I turn it on (a particular irritation with Bluesound OS).
There’s another choice which you may want to explore - J Play. I’m considering this as I’m also considering running HQ player to convert to native DSD - a format T+A DACs process particularly well as you likely know. There are some complexities to using J play as you’ll need some additional UPNP software but I understand the interface is quite nice and sound quality is not impaired.
I know a number of T+A users have taken this route and it’s discussed a fair amount over at audiophile style forums. Certainly worth exploring.
Best,