Having owned several of these amplifiers for ~30+ years and pretty much all the TOTL ES pieces from that era, and having 3 TAN77es amps right here in my lounge-room, I feel somewhat qualified to weigh in.
The meter ballistics, look and performance are excellent and more than a match for the relatively primitive meters McIntosh were putting on their gear at the same time.
The meters are
top-lit in two groups of three series connected 12V 100mA bulbs.
It is my understanding that McIntosh meters are true watt meters. At least they were in 1995 [compare:
Audio Critic Issue 24], measuring voltage and current, rectifying and averaging the product, and not just volt meters calibrated into 8 or 4 ohms. Not sure about Mac of that era, so I'll take your word for it. According to Ken Rockwell's review, the Sony meters, "read peak voltage directly off the internal signal output rail, calibrated in equivalent watts into 8Ω." But you are right, for the most part all meters are cosmetic, and decisions will likely come down to whether you like Binghamtom Blue or Tokyo Orange. Even so, once you spend dollars for them, you'd like them to work. And one thing's pretty certain, a McIntosh dealer will give you a loaner while your unit is in the shop. At least that was how it once was. Can't say that about my Sony dealer, back then. But I guess you pay upfront for this kind of service, and I admit I was going the cheap route, so what did I really expect?
As far as the meters being uplit or downlit, I was going from memory, and I have no reason to doubt what you are telling me. That said, they didn't stay on long enough for me to really investigate, and inasmuch as the amplifier was under warranty (which I didn't want to void), I never took the top off to check, or try home repairs. Wherever they were mounted, they didn't work reliably on my example, and other's units too. Interestingly, Sony soon came out with the TAN 80 ES, which (at least from the pictures I've seen) is the same thing as the 77, sans meters. I guess Sony decided it wasn't worth the effort to correct. The entire thing was an exercise in frustration. Sure, a light bulb doesn't affect the performance of the machine, but then why include them at all? Sony agreed.
So what do we have at the end of the day? A marketing thing, simply a cosmetic selling point. But it is the face a consumer sees from the get go, and as such it is important as a sales gimmick in these sorts of 'emotional' decisions. The fact Sony engineered something so simple so sloppily makes you wonder. Or at least it makes me wonder.
PS: I don't want to single Sony out for abuse. I've had other amps with shoddy build quality. The most egregious I ever owned was a small American boutique company, Amber, whose Series 70 amp kept blowing up. I got rid of that after two trips to the factory. Then they went out of business. Wonder why? I owned early PS Audio products that simply fell apart after a few years. But they were dirt cheap to begin with. Made Dynaco look like McIntosh. PSS: I was using the Sony amp with Acoustats, but found that Jim Strickland's 200 watt/channel Transnova MOSFET amp worked better, IMO. At least it didn't have meter problems!