You will miss the Thiels if you move to the Andra II. I would look for speakers that are more inline with the Thiel house sound that add more bass volume/slam/punch etc.
I listen to mostly rock and own Thiel CS2.4. I have being looking for the same reason that you have. I am coming to the conclusion that I want just a hint of bass coloration in the form of dynamic impact to drive the rock music.
With that being said I really dislike most speakers that I have demoed. You have to give up a lot of what Thiels get right in order to gain bass slam, or spend a lot of money and have it all.
I would demo the Revel Ultima line. The Salon go very cheep on this site and are the real deal. They will give you almost every thing Thiel's best speakers give and add bass punch and weight. I do think the highs are a little soft for rock music at some times but most people will love them.
Another speaker that sounds very good for rock music is the Sasha/Sophia 3 (they sound about the same...). They maybe too colored for you coming from Thiel. Yeah I just called the Sophia 3 colored and it is from an absolute perspective. They have a LOT of bass punch but it is a little peaky (in the room I heard them) and not as well integrated with the mids as Thiels 3.7 (never heard the 3.6). The upper mids on the Sopha 3 lack some the resolution compared to the 3.7.
With at being said the Revel Salon may be a good fit with great bass but more balance than the Wilsons (and better priced too). But I concider the Wilson line to be one of the best for rock music. It's colorations fit the music well. For me I will most likely move onto the 3.7, Salon, or maybe Kef 207/2 if I can ever get a demo...
Below I have added part of a review comparing the Andra II and Sasha.
"It is in the bass region where the Sasha scores a decisive victory that verged on being a vicious beatdown. The Andra IIs bass is very good, as far as it goes, which is to somewhere in the lower 30s in my current room. This room does not provide the assistive loading of the room in which I reviewed the Andra II back in 2002. The Sasha provided noticeably better definition and tautness and took that superiority into the very low 20s with consummate ease and shattering, floor-shaking power when called upon to do so. Here it was no contest: Sasha in a convincing TKO.
Through the mids, it was very nearly a push, with the Sasha inching a bit ahead. The Sasha's new midrange driver is truly special. As noted above, this unprepossessing-looking unit achieves a level of nuance and detail retrieval that has heretofore been the exclusive provenance of planar and electrostatic drivers. The Andra IIs midrange is, and remains, striking and exemplary in its honesty, and it took the Sasha to better it. The improvement is there, though it is marginal, but at these levels of performance (and cost) being marginally better is more significant than it is with lesser components. Slight advantage to Sasha.
In terms of the highs, the Andra IIs Dynaudio Esotar is perhaps my all-time favorite dome tweeter. Its airiness, precision and delicacy still remain at the top of the mark. Wilson Audio has worked wonders with its new version of the Focal Tioxid tweeter, to be sure. The Sasha W/P had definition and subtlety that were lacking from even the MAXX 2. The tweeter integrates better with its companion midrange driver(s) than any previous Wilson tweeter and provides musically excellent overall sonics, but it is not the last word in any one quality one desires from a tweeter, acquitting itself well across the board instead. Here, the Andra II wins by a heads length.
The Sasha consistently threw a bigger and more clearly defined soundstage and provided dynamics both great and small that few speakers anywhere can match. Overall, the Sasha was the better speaker in nearly every meaningful way. And well it should be"
http://www.theaudiobeat.com/equipment/wilson_audio_sasha_wp.htm