Hi, Unsound. :)
Any EQ applied via Roon is additive to any other EQ and filters in the chain.
If all your music was through Roon you could replace the Thiel EQ box with a Roon filter if you knew the proper parameters.
Roon is a little unusual in that it does all the DSP processing in the server, not the end point, so yes, any Roon-ready device should be able to take advantage of the DSP capabilities inside Roon if they are capable of the playback rate/type.
For instance, not all devices may support DSD, or more than 96 kHz, but if they are Roon-ready, then Roon can transcode up to their capabilities.
Best,
E