You'll be pleases to know it's pretty simple.
I assume your speakers are biwirable, i.e two pairs of terminals? Remove the shorting links before continuing!
Run a phono interconnect lead from the 370 'preout 2' sockets to the 'fixed' inputs of the 270. Leave the metal links on the 370's preout 1 sockets in place.
You can now biamp- use one amp for bass, the other for treble. If you want to bridge the amps, flick the bridge switches on both units with the POWER OFF! Then run cables to the appropriate terminals- you may need to consult the manual on this, although I'd imagine they'll be labelled on the back of the amp too.
Personally, these amps are mighty powerful anyway- I wouldn't bother with bridging just yet.