I want to send sound around a theatre with 8 speakers (in a circle, equally spaced), and 2 subwoofers.
What is the best (and simplest) object for the job?
I looked at ambisonics objects, but they seem too complicated for what I want. I have been using multiouts~ at home, but only have 2 speakers to test with here so can;t tell if it is good enough.
Is vbap a good alternative? With the CNMAT wrapper?
I can’t offer any advice on VBAP other than to point out that for each sound you position it will only use, at most, two of your eight speakers.
If you go with Ambisonics then try to use higher-order rather than first-order. With eight speakers in a circle you can use up to third-order. The problem with first-order Ambisonics is that the sweet spot (or area) is limited. In a theatre, it is common for people to be seated in a wide area with some of them up close to a speaker. If this is your situation then third-order Ambisonics should work better for you.
Having only two sub-woofers is a problem. For first-order Ambisonics you need at least three. There is some general advice on sub-woofers and Ambisonics over on the Ambisonia.com Wiki.
I can’t advise you on tools to use. Instead, you should ask over on the sursound e-mailing list. This is where the Ambisonic crowd hang out. They might also be able to give you advice on VBAP.