Yes they can! You can run fully balanced signals on the input. Connect "+" to R15 and "-" to R39. Leave out the ground lift switch. Both polarities are then terminated by 47k ohm (R25, R30), which you could change to anything you want.
It's a great way to do the input/driver stage. The current source in the tail forces a much improved ac balance, you can run XLR or RCA, you can float the whole thing dc-wise a volt or so in either direction (for long runs without ground loops). And if you use a low rp tube (6H30, 5687, ECC99), it can directly drive most output stages. It's just so simple I don't know why more amplifiers use it.
jh
