I don’t have a Mac, but own several tube amps and gobs of NOS and some new production tubes. My Dennis Had Insipre will run KT-88, 6550, EL34 and 6L6. The amp came with Gold Lion KT-88s. They are excellent tube IMO. Clean, transparent, linear with good balance and a touch warm. Rock solid construction, made in the old Reflector factory in Saratov.
You should also consider Shuguang Nature series KT-88-T. They take a while to burn in, but offer a touch more bass and detail. NOS Svetlana 6550 are an amazing tube, bass, midrange drive, and seductive. Less transparent but make music come alive, as in sitting in the front row.
I don’t own any new production 12AT7s, all NOS. But I do have a Gold Lion 12AX7 Russian gold pin, that is V1 signal tube in another amp, great tube. Just like the KT-88s, clean, transparent, well balanced. Be sure to get Russian version, they also offer a Chinese version. It’s a bit flat and uninspired. If you want to chase NOS, go with Telefunken or Amperex.