As everyone else here, I have been through this journey with fairly intense involvement (I mean spending on average at least 3-4 hours every day) and making changes (after careful research, audition, discussion) over period of 4 years to ultimately get my current set up (still not 100% yet, but quite there: always room for improvement). In my opinion changing different components has major impact on certain very key factors: I have spent ample time and money on every component diligently (speakers, amps, preamps, dac, streamer, cables, footers, stands, room treatments), I mean a lot of experimentations (changing one component at a time to know exact impact of each). You have to follow logically, else, you get frustrated. I am not telling you have not done your part: In fact, I am assuming you might have done better than me.
Having said that for soundstage, besides speakers and amps, biggest and major factor playing huge role is Room treatment: I learned this painfully and expensively. Trying to change gears after gears with some (but not major) impact, until I paid good time and attention to room treatment. Room treatment can make expensive gears sound cheap (or politely put suboptimal). I am sure you have done your room treatment, but if you are struggling with soundstage, I would pay attention to room treatment again. Changing electronic gears (preamps, dac, streamer) does change soundstage, but they do change more of tonality (and other characters which I am not going to talk). Another important thing to help with soundstage (can compensate for suboptimal room treatment) is addition of subwoofers (I am not using it, as I have had very good results with my room set up without subwoofers). I was heavy SS guy and now I am all tube guy.
Just to be pre-amp specific: I have tried a bunch of tube and solid state Preamps: ultimately ended up with Aries Cerat. They are very expensive, but in my opinion, end game gears. If your budget stretches, try them or hear them. I have Aries Cerat Kassandra Mk2 dac and incito S preamp (eventually will change to ageto preamp and ianus essentia amps).
My response is based on my observation in my set up. Ultimately, music is subjective and you change things to make your ears happy/ satisfied. There is no right or wrong answer: just preference.
I am very busy lately and have not posted for a while. I am on vacation now and thought to help out our fellow friends who are going through this "audio/music nirvana". If I don't respond again, it is not I am ignoring or rude. I just have enough time in my plate. Remember it is "your ears, your money and your music".