You can see my comment regarding headphone and speaker volumes with my 8030Cs in the 8030C review thread. I'm including a quote at the bottom of this post.
https://www.audiosciencereview.com/...8030c-studio-monitor-review.14795/post-701547
I am using a different DAC/amp/preamp setup than you, but I was able to get my headphones and speakers at kind of a similar volume level. I briefly had an 8020D for a week before upsizing to the 8030Cs and I think a similar volume result could be achieved. The JDS El Amp II preamp output ranges from 0-2.0VRMS (that's what JDS told me). When I was listening to Tidal earlier today, I probably had my preamp volume knob between 9 to 11pm. I think I have volume normalization turned on in Tidal, but regardless, some recordings just seem quieter, and some songs are nice when the volume is cranked up.
I agree with some of the other posts that getting a comparable volume match from one device with a combo headphone amp and preamp out might be hard to do, although I'd think it would be possible if you can adjust the sensitivity on the powered monitors and you use the same pair of headphones on a regular basis. Fortunately the -6db to +6db range on the Genelec 80X0 series works with my preamp setup. I'm happy enough only having to turn up the knob from 9 to 11pm for most of my listening needs. When I briefly had a pair of Focal Alpha 50's prior to getting the Genelecs, I could barely move my preamp volume knob without getting to very high levels. That was a dealbreaker. The Genelecs do have a limited sensitivity adjustment range compared to some other monitors (I'm not sure if there is a good reason for that), but as I mentioned, it's just enough range for me. It would definitely be cool to have more range though. The white "home" series of the 80X0 have a different input sensitivity via the RCA inputs.
I'm guessing you won't want to change your other system components, but if you don't care about getting a DAC with dual outputs, you can get a JDS Element II and have a good DAC and great headphone amp, all in one box with a great volume knob. Another thing I like about the Element II or El Amp II is that you have to hold a button on the back to switch between preamp or headphone mode. I greatly prefer that than units that play the headphones when headphones are plugged in, and require the headphone to be disconnected to use the speakers. That said, there's also an argument for getting something like a Motu M2/M4 or other unit designed for use with monitors.
Here's the relevant part of the post I mentioned:
"With my JDS El Amp II and the input sensitivity on the 8030Cs set to I believe +6DB, I think 9 or 10 on the El Amp volume control has me at jamming levels. The amount of volume control I have seems granular enough to me. It's also nice because the SPL from the speakers at that volume control level is similar to how loud my HD650s would sound if I had them plugged into the JDS. That means I don't have to think about making sure the volume isn't too loud if I'm alternating between headphones or my speakers. I usually use my Bottlehead for headphone use, but not always."
