I have not auditioned the drivers you consider (and I would not trade my 2245 for any of them) but maybe some general considerations: Two drivers offer some flexibility:
- you could run them in a stereo mode in two enclosures if you want
- bass is in most cases the result of woofer and room modes. Two drivers may give you more flexibility with your room acoustic
- you could build one subwoofer "impuls-compensated" to reduce enclosure vibrations
Having said that, the "Seismic" from Quint Audio (German Aurasound Distributor) is said to be a "beast"...
Stefan