Midrange Increasingly Harsh

Yep, I’d do a full re-tube. Your power tubes are definitely shot and the pre-amp tubes are at the end of their life. Try to avoid using it until you get the power tubes replaced at minimum as the distortion from spent tubes can damage the speakers. Fortunately you don’t play at high volumes so hopefully the drivers are unscathed.

Congrats on averaging 1k hours a year of listening! That’s tremendous. I work from home and even then I doubt I’m half that.  I think I'll do some listening now and try and catch up lol. 

Even if it is not the tubes getting worn, it is helpful to have a full complement of replacement tubes.  Any time you suspect tubes are going bad, you can then do substitutions to see if that cures the deterioration.  Even when you don’t hear an obvious problem, performance can decline gradually and you may not notice this until you do substitutions.

Make sure ears are clean before passing judgement on gear. 

OP mentioned the problem persists from BOTH CD and TT, sooo, that rules out source equipment.

It is unlikely both speakers would develop problem(s) at the same time. So, simply switching speaker wires, left to right, right to left, NO OTHER CHANGES: IF the problem moves to the other side, it's that speaker.

Tubes: get paper, make notes, easy to confuse yourself or forget. Swap all tubes L to R, problem move? Next: using tubes from the 'good side', swap l/r one at a time, any single tube swap make a difference?

Many tubes last 10,000 hours, so 5,000 hours is not a DEFINITE answer. Ask seller about the tubes you bought from him, what are the life expectancies of the tube types your unit uses?

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How many times have I advised a simple tube tester to give answers when problems occur????????????????????????? Blindly buying tubes is an expensive shot in the dark.

I did some side-by-side testing yesterday and discovered that there is no difference between the left and right speaker.  I swapped cables and no change.  But when I changed from the eight ohm to four ohm output, the harshness decreased somewhat.  My bride couldn't tell the difference.  I got in touch with Upscale Audio and ordered a set of Tung-Sol EL34B power tubes.  We'll see how that goes then get some new 12AX7 and 12AU7 tubes.