I already have the two cabinets, but the TD15 model I am looking at will work in smaller cabinets. As you know, going smaller in size always demands a compromise somewhere. My cabinets are slightly undersized for the SI drivers, but will be slightly oversized for the TD drive units. This will result in a change in the system as a whole from a high Q system to a lower Q one. This is another element I want to change. I'm chasing sound quality above all else and 4 of the TD woofers will match a pair of the SI 15s for output down to 20hz, which if I am honest is eough for my requirements and satisfaction. Part of the reason for all of this is that currently my system suffers from 3rd order harmonics (some of which I am sure is attributable to the room) and I can hear this quite clearly during certain scenes. I've already sold the drivers, but have them for some time before they have to be moved on, so I'm looking for a suitable replacement. As long as the replacements can meet my output criteria, namely 105db flat to 20hz, then I'll be happy with them. I was hoping to buy the new AV woofers from AE, but being based in the UK they are prohibitively expensive. The TD woofers in this respect are nearly half the price. I cant make new larger cabs for the drivers I have now (Though I could try one driver per cabinet), so my choices are smaller cabs, or a suitable replacement driver that will work in my current cabs with a lower Q value, a driver that will work in smaller cabinets, or dropping to 12 inch drivers. I've been looking at the SDX12, which seems similar on paper to the SI driver units, but again shipping is quite expensive. One last thing I like about AE drivers is the focus on low inductance. I used to own the original AV15s and to date they are the best driver for quality I've owned, so a desire to go back to AE comes from that as well.