might sound dumb..

[Johann]

well, you'd run the rockerverb into one of the cabs, and then out into the poweramp which is connected to the other two


shouldn't be too hard

[rick.heil]

Ok, to preface all this, I'm going to link to the manual (look at page three of the PDF) so that other people can look at what it says and double check what I figure here.  manual

Apparently, you can connect one 16 ohm cab to the 16 ohm jack OR you can attach two 16 ohm cabinets to the 8 ohm jacks (one each).  Or, you can connect one 8 ohm cabinet to one 8 ohm jack, but not two 8 ohm cabinets to both 8 ohm jacks.

Ok.

This leaves you with a few options (in no particular order):

#1:  You could hook two of the cabs together and get 16 ohms.  BUT FIRST! Check the back of the cabs to see how they connect, if it says "series" you're golden, if it says "parallel," no such luck.  It may depend on the brand of the cabs, and you could probably change it if you had to (we'll ignore that option for now).  I would then hook the effects out to the input of your power amp, which cn then run the 2x15 cab.  Make sure that you don't need to loop back to the effects in (you might need to, I usually don't use the effects loop jacks on my amp so I'm not positive).  If you do, you could probably get away with using a splitter cable.

#2:  You can run any one of the cabinets off the Orange head, then use the same effects loop setup to run the other two cabs.

Ok, I've read it a few times and I think I got everything...