Need to build a headphone system

Given what you’re looking for I’d highly recommend the Hifiman HE1000 SE and the Quicksilver tube headphone amp.  The HE1000 SE rivals their $6000 Susvara headphones but are MUCH easier to drive and can be had for only $2799 ($700 discount) from their open box section on their site (I bought both my ‘phones from there and couldn’t tell them from brand new).  The Quicksilver amp can be had for only $1198 and is a huge value and would be a great pairing with the HE1000 SEs. So for $4000 you could have an awesome HeadFi system that rivals the best.  Here are a couple reviews FWIW…

https://soundnews.net/headphones/full-size/hifiman-he1000se-review-how-high-hifiman/

https://www.head-fi.org/showcase/quicksilver-audio-headphone-class-a-triode-transformer-coupled-single-ended.25701/

Best of luck

If you want to think outside the box, literally, I could recommend the RAAL SR-1b earspeakers (nearfield ear monitors) with the Ti-1b transformer interface box.  You would need a headphone amp with a 4-pin XLR output that delivers a minimum of 2 wpc into either 16 or 32 ohms, so a pretty powerful headphone amp.  But there is nothing like the SR-1b in terms of spaciousness, speed, detail, and transparency with the RAAL ribbon drivers, and they should fit with your hearing aids since they have a pad that goes behind the ears.  Maybe not.  And the system should be within your budget.  The only downside is bass quality instead of quantity so some folks who like gobs of fat bass probably won't like the SR-1b.  Check out the RAAL Requisite website for more details.

http://www.raalrequisite.com

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.