The AR is a solid tt. I owned one with a Premier MMT arm for a few years. I replaced it with a VPI W19 MK3 with Grado arm, and in my opinion the overall improvement in resolution, bass extension, and overall refinement was very significant, and not subtle. What the AR did have, in comparison, was a nice sense of drive, or prat. But the soundstage was smaller, the sound less weighty, and a little cloudy in general. I would rate your Rega arm as superior to the Grado arm; so add that to the mix. A friend has that HW19 with a Rega arm, and the sound is very good. IMO, in a different league than what I had with the VPI/Grado combo.
My advise would be to keep the Rega, and mount it on a VPI HW19 Mk3, or better yet a MKIV. For an investment of well under $1000, you will realize a very significant improvement in sound.
Good luck.