Tube reliability in amps

I am contemplating the purchase of a tube power amp. I already have an Audible Illusions pre-amp, which has given me virtually no problems tube wise. I would like to hear from a bunch of Audiogoners on how long power amp tubes last in the real world, do I have to keep matched pairs or sets around or can I just replace one? Also I have B&W matrix 804's and I have been told tube amps are not a match for them or that I need a lot of power (read expensive tube amp). Wavering between tube and SS, HELP.

PS. I listen to orchestral music and piano. Sometimes loud like about 90 db.

Thanks