I'll caveat all of the following by saying while I am a lifelong music lover, I have only recently returned to the earnest pursuit of HiFi equipment. This present HiFi journey started in November of last year when I purchased a Lumin X1 DAC. Once purchased, I tested it going directly into Bricasti M25 and Lumin Amps, with and without a Nagra Classic pre-amp. In both cases, I preferred the preamp in-between. I also tested going into a Pass Labs X150.8, with and without an XP22 preamp. In the case of the Pass Labs, it was closer but I still definitely prefer the preamp. In all three tests, using a preamp added more warmth and richness. The step-up in overall power/volume level with a pre-amp is also better in my opinion. In the end, I settled for the Pass Labs amp and pre-amp. I have not used or listened to a Bricasti DAC, so I cannot provide any help in that aspect.
In general, I like the convenience of using my iPad to control the programming, so I've pretty much settled on using the Lumin app to control volume, as well. Therefore, I set the XP-22 at unity gain (89) and control my listening volume with the Lumin app. I have done some experimenting with using the XP22 to control volume while adjusting the Lumin X1's Max Volume %, Leedh processing on/off, and analog audio output level. Not a rigorous test, but just enough to get an idea of what might be possible. With that brief encounter I didn't find any particular setting that justified not using Leedh processing, setting the XP22 at unity and controlling volume on the Lumin App.
In summary, my opinion is yes to a preamp and yes to controlling volume with the Lumin app for your primary listening room and system.
I think it’s important to consider how you are sourcing your music as well. Are you only playing local digital files or do you have additional input services and/or devices such as a turntable (with or without a separate phono stage), CD, etc.? In my case, I am only interested in my local digital files, hosted on my NAS. I am not streaming from the online services like Spotify or Tidal. However, I also have a Sonos setup which is accessing the same files on my NAS and streaming throughout my house, both indoors and out. On those occasions having the preamp makes it possible to use a Sonos Connect to go into my XP22 and listen via the Sonos or IOS music apps in my main listening room, in sync with the other locations. Again, by having the XP22 set at unity gain, I can control volume in the main room and all rooms with the Sonos volume control. To be clear when using the Sonos, I am not listening through the Lumin X1 in my main room. I’m just saying it was another justification for a preamp in my particular case.
FWIW, my NAS has an aggregated 4GB connection to a Cisco GB switch (52GB backplane) and the Lumin has a 1GB SPF connection to the switch, as well. The Sonos Connect is using WiFi. With only a few exceptions, as one might expect, listening through the Lumin X1 is markedly better vs streaming those same files via Sonos into the same XP22 preamp. There is just no way to sync the two, so if I need multi-room listening and want my main listening room to be in sync, I need to switch inputs on the XP22.
IMHO, there is still no app with a good interface for managing digital files. I think the user interfaces of the Lumin App, Roon, Apple Music App, Sonos App and Limn all are unintuitive, kludgy and frustrating. The Lumin App makes it very difficult to just go to an album directory and play an entire album (A couple months ago you couldn’t do it all. Now, at least you can, but figuring out how to do so is a challenge and clunky). In almost every case, whether sorting by directory, artist or song, it always seems to be tedious to find what you’re looking for and just play it. Once you’ve created a playlist in one app, it’s not usable in any other.
I understand that everyone will have different approaches or opinions on how best to display a library of music. I also understand that lots of people use streaming services in addition to their libraries, but as a former software developer I feel like there should be a better metaphor for allowing one to display and select what they would like to listen to. I could go on, but I’ll spare all of you my rant and end on that note before I go too deep down the rabbit hole. If there is a good discussion thread on streaming app UX, please point me to it. Thanks.