I don't think they'd need to strip it too much - mine's very dark brown and I've had it dyed fairly red.
I had chunks of mine died literally pillar box red once, and they had to bleach it within an inch of its life first. Saying that, I was just careful about always conditioning it, and it only really lost condition when it was growing out (ie hair about level with boobs). Have also had less extreme reds, with no prior bleaching (although there was amonia etc in the dye), and had a similar thing - condition not affected until it got a lot longer.
Why don't you try a henna block from lush they do a bright vibrant red then it will fade if you get sick of it or dont like it. If you do like then you can keep using a couple of squares every 6-8 weeks be warned tho' it is very messy but gives a lovley shine I use the caca marron and leave it on all day if I can. Sorry dont have any experience of having it dyed at the hairdressers
Thanks- got a glut of rasps in the garden so I made one! was yum. I did my hair with 2 squares of the cacca marron on Sat left it on 7 hours and tbh didnt do that much-am redhead but is nice and shiny gonna do the full block next time