I find the Usher TD-20 to be a very warm and lush speaker. Going from the Rowland to the Gryphon would add even more of this, which could be too much of a good thing. One thing that allows the Usher to sound less warm is having enough space for it to breathe. Even though they are front ported, I’ve found they sound best with at least 5’ from front wall to the back of the speaker. The big drivers require the airflow behind the speaker. If you are already providing it with this kind of space and the pairing Rowland delivers too cool, neutral or in your face sound, the Gryphon could be a contender. The Gryphon will deliver a refined Class A experience that may make the sonics feel more human.
In my experience Usher DMD series can be lovely if paired with the right gear and in the right room, but it is hard to get the best out of them. Try to see if you can demo the Diablo to be sure.