Need to build a headphone system

Go for the RAAL SR1b, at least on a home trial.

You could try out the SR1b with a $300 Schitt Jotunheim R RAAL amp (if you can still find one). Use the Star8 cable with the JR.

If you want to spend a bit more, the best amp for the RAAL is the VM-1a. It is a $7K tube headphone amp and really is the perfect match for both the RAAL SR1b and CA-1a phones. The SR1b sounds more like 2-channel and the CA-1a is more like headphones. With the VM-1a amp the CA-1a is incredibly dynamic. I think even bass heads would like it.

Word is starting to get out on the 2-channel community.

Oh, dear, the CA-1a is again something else! The HD-650 was already a bit of a revelation, but the RAAL quite simply steps up the game to an entirely different level. The increase in resolution is unbelievable, as is the further increased transparency. It’s that I know I just put on a headphone, but honestly, this had nothing to do with headphone listening in any way that I had experienced before. Jeroen is a more seasoned headphone listener than I am but he was as amazed as I was

In many ways, the CA-1a reminds me of Magnepan ribbon speakers, only with no crossovers and no room issues. Interestingly, that comparison also extends to the bass where the CA-1a is extremely fast and sublimely accurate, but not particularly robust or full. In fact, the entire frequency range is abundantly free from coloration and thickness, and the bass was simply no exception.

SAEQ Hyperion Ge and RAAL Requisite CA-1a | HFA - The Independent Source for Audio Equipment Reviews | Page 3 (hifi-advice.com)

The CA-1a is not even the best RAAL phone and the one that 2-channel folks should hear, that would be the SR1b.

Greetings, and welcome to the headphone community. I dove into head-fi in 2015 when I moved to Japan. I too, have listened to many headphones on the market.

The previous two suggestions, the Woo WA5 with Sennhieser HD800S is a very good suggestion along with RAAL SR1B. I have listened to both many times. Both come from two opposite sides of the spectrum to reach what you are looking for. I would definitely do your research and listen to the RAAL system prior to purchasing. This is not a HP you buy unseen. As far as the HD800, yes I truly believe paired with Woo products decreases the brightness and provides a very good listening experience. Personally, I would not purchase the HD800S unless you pair it with a warm sounding tube headphone amp like the Woo. I believe both HPs will work fine with hearing aids specially the RAAL since you can adjust the wings.  

Now, let me throw in a 3rd suggestions, which will provide you yet another polar spectrum close to your price range. A electrostat system consisting with the Blue Hawaii SE (BHSE) and electrostat HP of choice. I am currently a proud owner of the BHSE with the Audeze CRBN. This system will run you 10K, but you can shop for a HP within your price range such as the Stax 007 Mk2. Now, electrostat system naturally is notorious for being analytical specially pairing with Stax, hence why I own the Audeze CRBN. Although, with the BHSE you can swap out tubes as needed to reach your desired listening pleasure.

https://www.headamp.com/products/blue-hawaii-se

The HeadAmp website will provide you info on the HD800S, RAAL and the BHSE with electrostat HPs. Not sure you location of residence, but I would recommend visiting https://thesourceav.com/ in Torrance CA. This is one of the few places where you can listen to all three suggested systems. Spent many hours in that place.

Good luck, and again welcome to head-fi.

P.S. If you ever come to the decision to purchase the BHSE/CRBN combo, speak to me and I may cut loose my personal system for your price.

Thank you all!  This is is all really helpful.  I'm in New York.  Does anyone have experience with Audio46?  Although I expect there will be lots of home trials, a good store would be helpful.  (And FWIW if I find what I want in a store, I'll buy it in a store - it's hard enough being in business without being a showroom for the internet.)  I am partial to tubes, so I'll be checking out Woo and the VM-1A for sure.  This is going to be fun! 

The best place for RAAL info is head-fi.com, where Danny and Alex the 2 principles of RAAL-Requiste help out.

Raal Ribbon Headphones - SRH1A | Headphone Reviews and Discussion - Head-Fi.org

RAAL-requisite CA-1a Circum-Aural Ribbon Headphone is here! @HeadAmp | Headphone Reviews and Discussion - Head-Fi.org