I just put 2 Eminence Commonwealth 12" Speakers in my Twin so that I can use my twin as a backup amp as well as a preamp for my rig.
When stacked vertically with my HT 2x12 underneath, it makes a monster 4x12 column! The Eminence speakers sound a bit brighter that the JBLS in the HT cab, but they sound great! I am very happy with them.
No I can use the twin two ways:
preamp > Mcintosh > left channel HT Speakers, right channel Twin Speakers
Or just as a twin with the extra speaker jack going to the HT (or not
Nice to have the options!