It looks like there will be two options.
The first is a woofer module that is essentially the same as the SoundScape laid on its side with the passives at both ends. The top section would then sit on top of this cabinet. So you have exactly the same drivers all around. It would be about 30" high, 28" wide and 23" deep. The F3 would be the same as the SoundScape model it was meant to go with (SS10 or SS12).
We are just starting work on a second, smaller and lower cost center as well. This will use a pair of 7" woofers in a front-ported cabinet with the Accuton and RAAL in the middle (a WMTW configuration). This one will probably end up being about 12" tall rather than the roughly 30" tall option above. This 3-way will have an F3 of around 30Hz.
But to answer the question first posed, an HT2 center with the RAAL tweeter would probably work just fine as well.
- Jim