going from tube preamp to solid state

I would do it just on principle.  What principle is that you may ask?  The principal of the boiling frog.  

Tubes degrade over time.  SS much, much less so.  I own Tube and SS equipment; amps and preamps.

Every few months I will switch between SS and Tube for some comparative listening to assure that my tube equipment has not slowly degraded in sound quality.

And in fact I was prompted to buy some new tubes after the most recent switch test...

Sounds like the soundstage issue is a big problem unrelated to tube vs solid state.  You might start out by discussing this issue with the manufacturer.  I’m assuming that in treating your room that you did basic things like damping first reflections.  ghprentis Is always a great resource and his suggestion of posting a room photo might be helpful.

I have had Schiit Freya + preamp and then Esoteric then SPL Director. The director also has a DAC that I don't use but the preamp is the exact same as the SPL Elector.  Here is a great review on how good it is.

http://v2.stereotimes.com/post/sound-performance-lab-spl-elector-preamp--performer-s800-amplifier-and--m1000-monos-by-terry-london

Just my personal experience.  I thought I’d never go back to SS for my pre until my Luxman started acting up.  I’d always wanted an Audio Research pre and figured this was as good a time as I was likely to see.  I’ve been using the ARC for about 6 weeks now I guess and don’t feel like I’m missing anything at this point.  Power amps are still tubes, so there’s that.  

There’s a little bit of an elephant in the room I believe. You are much more likely to be able to adjust your soundstage and imaging with different speakers than any kind of preamp changes. Possibly you just love your PBN’s so now you gotta find what works with them . I think if you changed speakers you might find that is the path to you desired sound