going from tube preamp to solid state

Try the Sanders “the preamp”

Nad - pre is,nice, but gets warm, make sure it is ventilated on top

parasound p5

adcom preamp

used Onkyo p-308 - may need additional 180-250$ have a good tech open, replace,caps with higher quality, clean everything. A warmish sound to Onkyo, gives depth to music.

most Integra Onkyo are a good quality preamp.

probably get one for a few hundo

If you are looking for a straight wire with gain kinda preamp that projects a huge, transparent, and open 3D soundstage, look no further than this.  If it doesn’t work you can turn around and sell it with little/no loss.  I owned their BP-6 with a very similar architecture and it was fantastic.  Well worth a try IMHO. 

https://www.ebay.com/itm/225429657659

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