Re: Power amp for Line 6 rig?
Are you looking for something that should add its own sonic stamp, or merely clean power? For the first I would go with solid state, for the second tube. Solid state will give you greater control evenness of sound over a range of volumes, and should let the modellers themselves shine through more; a tube power amp will colour all modelled sounds so they sound more alike, but give it more of the feeling of response you'd get from a normal power amp. I would probably lean towards solid state, but there are people here who swear by tube power amps as well.
If you are merely looking for clean power, I think you could do worse than the new SD PowerStage 170. This is small (since it is class D), light and has a three-band eq to help fine-tune the tone. Note that the power amp will be slightly more powerful than the speakers, and could blow up if you dimed it; be careful when you go above 12 o'clock on the volume knob and everything should be fine (for this setup the speakers should be wired in parallel).
For rack power amps the Rocktron power amps, and especially the Velocity series, has long been standard. Keep in mind, however, that 95% of the rack power amps you will find are stereo power amps, that is, effectively two separate power amps, so that you may well be getting the double of what you need.
If you want a tube power amp Marshall and Mesa/Boogie both have models that often are used, with Fryette being the most common boutique choice. Please note, though, that power amps using EL34 or 6L6 tubes rarely come in lower powers than 100w (and we all know they produce a lot more when dimed) so you may run into the same matter as with the PowerStage here.
I hope this was useful as a starting point. If you favour one of the approaches above over the other, I might be able to help you out further.
(Full disclosure: I have not tried the PowerStage yet, but I will hopefully be buying one for my guitar synth rig soon)