SigmaTel C Major Audio configuration help needed on Xubuntu, redux.

Recap and extension of this post (or this one) from July:

Freda's computer is her mother's old Dell XPS M-170 gaming laptop. (This is identical to the Inspiron 9300 but with glowing blue bits on the lid.) I put Xubuntu on it. This works perfectly, including sound (SigmaTel C Major Audio) ... but controlling the sound is proving problematic.

There are three speakers: two tweeters in stereo at the front and a woofer in mono. In Windows, these all work together. (You can't change the balance per-speaker, but at least they all go.) In Xubuntu, the sound control panel lets me put sound out either the treble speakers or the bass one, not both at once.

I cannot find how to switch on and balance all speakers at once, as I wish.

I investigated various ALSA manipulations. PulseAudio appears to be deciding which output ALSA sends all sound to as hw:0,0. So no ALSA twiddling appears to have an effect — ALSA just can't see the separate outputs.

pavucontrol lets me switch either the mono woofer or the stereo tweeters on, but not both at the same time.

lspci line:
00:1e.2 Multimedia audio controller: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6 Family) AC'97 Audio Controller (rev 03)

Pulse, however, can tell there are two outputs and even identify them to me. It just won't let me switch on both at once.

So my problem appears to be how to tell Pulse that both speakers should be used as the sink. How do I do this? How do I find out how it identifies them? And where do I tell it?