Actually, the EXT predated the HT2's.
When Adire announced their new Extremis drivers, we thought we'd take a look. It turned out that they had very good bass extension. So we did a floor-standing MTM design using them. It turned out very well, but a short time later a couple of customers indicated a desire for a similar model using W18 drivers instead. So the HT2's were developed.
While the W18 drivers cost more, the difference in cost between the speakers is negligible. The W18's are more detailed and, thus, result in what we feel is a superior speaker. The only area the EXT's excel in is bass response. They do play lower.
For someone who likes deep bass and is not that interested in midrange detail, the EXT's would be a great choice. For example, if you only listen to rock music which is usually highly compressed, the EXT's are probably a better speaker. They are more forgiving where bad recordings are concerned. But in most other cases, the HT2's would be a better choice.
By the way, work is proceeding on your V3's. We hope to begin finishing them this week.
The EXT's are a 4-ohm design.