BOSOZ requires 10k pots. 50k might be too high.
TKD and Alps will work. You'll need 4 monos, 2 stereo pots or a 4 deck pot.
Discrete stepped attenuators are the way to go. Discrete costs more, but you'll know where your money went. On the low end of cost, 4 mono wiper type pots will probably be more accurate since you can dial them in independently.
Log pots are ok. They are configured to have an increase in volume that's more natural to our ears. Linear will work, but when you turn it up, it will be a more abrupt volume adjustment.
Adjusting the gain isn't hard. I don't know how to do it. Probably require scaling the a pair of resistors. one of the resident rocket scientist could probably figure it out easily by looking at the schematic.
