Thanks for helping, have done a bit more research and think what I actually need is a 2 channel
preamp with S/PDF output and a coaxial cable. Would this be the way to get 2 extra inputs?
Yeah, You've pretty much got two options.
A two channel pre will (obviously) give you two channels. Ie, two mics.
If that's enough to cover your toms then that's fine.
They will, of course, be discreet so it's just the same as having two extra channels on your interface.
If you go the other road that you mentioned in your
original post then Manslick has you covered with that image.
This is only really worth doing if you intend to use (and sum) more than two microphones as he's doing.
Unlike with discreet inputs, this setup relies on you getting your sound and balance right at the time. There's only so much you can fix in the DAW after, see?
The panning thing comes into effect with a mixer in the chain so I guess I'd be panning one tom hard left, on hard right and one dead centre.
That gives you a little bit of
control after the recording, but not a massive amount.
At very least you could increase/decrease the stereo image of the three toms by adjusting how wide panned your stereo track is in your daw.
Hope I'm not stating the obvious here. I forgot you
originally mentioned mixers in your OP.