I'll assume that your Acoustimass system is a two channel unit, so I'll respond accordingly.
You can use it as a stereo pair, but you'll have to use it and hook it up as a complete unit, that is as a pair of speakers. Placment might be an issue as all the bass, mid bass and part of the midrange will be eminating from the bass toaster. This might work well as rear surrounds, with the bass toaster placed somewhere in between them.
As far as flanking speakers, they will function but you'll have to run both sets thru the bass toaster and, from there to the individual satellites. Again, all the "bass" will be coming from one location, probably on one side of the room or the other. If this is acceptable to you, then go for it.
If you are using them as "presence" speakers (mounted in the front, between and above the L/L/ pair, them this might be acdeptable as I don't think these require quite the bandwidth of the other speakers.