Hi Outlier,
In your case I think is time to buy new tube's, since your are the second owner and you been enjoying the amps for a couple of years now using 89db speakers which I think you be run out the tube's life quicker than a 92db speakers. Also Alfred at KR Audio products is a very nice guy to deal with and is a really helpful guy too.
I'm not a PRO but you should keep your amp's in the same wall outlet if possible, that way you get the same result. Later
Bernie