I posted a response in my system description but here are some further thoughts. I don't think tube usage would be an issue with the Ref5 unless you leave the preamp on all the time. My Ref40 warms up in an hour and doesn't sound much better after that. The signal tubes will easily last 5000 hours and are not that expensive.
If set on Pass, read the description of the Xp-20 v. Xp-30 here at dagogo:
http://dagogo.com/pass-labs-xp-30-preamplifier-review
The XP-30 would be my choice if you wanted to go with the Pass preamp.
As another less expensive option, I don't know whether you have tried different tubes in the LS22?
I also found this article of interest. I have tried these specific types of mods in other equipment with terrific sonic results but few people have the skill or want to damage the resale value of their stuff:
http://www.10audio.com/arc_ls22.htm
Good luck!
If set on Pass, read the description of the Xp-20 v. Xp-30 here at dagogo:
http://dagogo.com/pass-labs-xp-30-preamplifier-review
The XP-30 would be my choice if you wanted to go with the Pass preamp.
As another less expensive option, I don't know whether you have tried different tubes in the LS22?
I also found this article of interest. I have tried these specific types of mods in other equipment with terrific sonic results but few people have the skill or want to damage the resale value of their stuff:
http://www.10audio.com/arc_ls22.htm
Good luck!