OK, here's the solution for your tech.
The 2SK244 is a Sony designed dual differential 8 pin SIL containing 4 FETs. I think they had it fabricated in the late 70s, so they must have had a big pile of them. They used it from the early Esprit preamplifiers and clearly had plenty of the parts left over even into the early 1990s because many of the 80s/90s ES TOTL models used it.
I have come across noisy ones in the past. Sadly, they are essentially unobtanium now. The TAE77es/d preamps use them, as does the Esprit TAE901 from 1981. Also a bunch of integrateds, TAF555es/444es IIRC.
But here's the deal. A funny thing happened between the TAN77es and the TAN80es power amps (2 years approx apart). Sony must have run out of 2SK244s, so they changed some resistors (R310/311 from 22ohms to 47ohms and R303 from 120k to 150k) and dropped in an NEC uPA68H into the same place on the PCB. Yes, it has one less pin, but two of the pins weren't used on the Sony K244 install in the N77es. The centre pin on the 7 pin uPA68H is substate and not connected- it is an easy drop in.
You can find uPA68h all over the place. Get NEC originals from a reputable source.
TAN77es front end:
TAN80es front end:
block diagram 2SK244:
**If your tech changes to the uPA68H, make sure he does both channels exactly the same, especially if you want to use the BTL mono function of the N77es.**