To put it more directly. To me, the Sierra-2 is the more impressive speaker compared to the RAAL Tower, even though the RAAL Tower is decidedly the better speaker. Some might disagree, but at least to me, given the size difference, what impresses me most is just how close the bookshelf comes to the tower despite all it's disadvantages.
I appreciate your comments. You own Ascend both towers and Sierra 2 and are much more knowledgeable than I am. Nonetheless, I stand by my perspective. Based on his original post, the way he listens and the size of the room he is going to want towers. He should start there. If the towers give him the extra SQ he is looking for in music (which I suspect they will) he can fill out the rest of his system. If not Ascend is not for him and he can send them back. I also think this approach gives him more flexibility in how he builds out his system. The Horizon is not inexpensive, he would have the option of not using Sierras in the back possibly using 170s or HTM and using the extra cash for Horizon or subs.