RWD, you have a very nice analog front-end working for you now, so I'm just going to ramble a bit with some thoughts to share... If you really like your Rhea, you will find similar sonic qualities in the Calypso, or better yet, the Callisto Signature. In my listening experience, the Aesthetix gear evolves from a different set of listening priorities than the ARC. For me, the preamp always has a huge impact on the overall character of the system. (And, if you were to make any move from your Rhea, I'd recommend you consider shifting to the Io Signature rather than any of the other phono stages mentioned. But I agree with your sense that moving from the Rhea is not the thing to do.)
There are many things that the VPI turntables do very well and I can join you in your respect for Harry's work. A number of people whose listening accumen I respect have said that they actually prefer the TNT Mk.6 to the HR-X, and a member of our local audio group just made the choice to go with the TNT6/JMW12.5 after a lot of consideration between the two. (The TNT is reported to have a somewhat fuller, slightly warmer sound than the HR-X with a more fully fleshed out harmonic structure versus a leaner, somewhat more direct presentation from the HR-X.) With your Aries, consider what can be gained from some updates (bearing, platter, 300rpm motor), including the new wiring update for the tonearm. And consider the TNT Mk.6 with JMW 12.5 as an alternative to the HR-X. Also consider moving from the SDS to the Walker Audio motor controller for a futher improvement.
As you look at options for improving the sound of your system, don't lose sight of your cartridge. The Benz is a good cartridge, but incorporating a cartridge at the performance level of the Magic Diamond, Dynavector XV-1s and a few others might well make more of a difference in your enjoyment of your system than any other change you've mentioned.
Consider whether you've fully extracted from your current system all that it can deliver. Over 35 years, I've often lost sight of this as I've gotten interested in seeking out that next great piece of gear that will move my system to the next level of performance, only to again be amazed at how much improvement I achieve when I've focused on the small things that incrementally combine to make huge improvements. So, let's just assume you've already done all of the small things we talk about such as: applying Extreme-SST at all connections, installing dedicated circuits, using top quality receptacles (like Walker Audio/Jena Labs/Porter Ports), resonance control, room acoustics, etc...
Good luck in your deliberations!
