Is the LS a good idea in a HT?
I do not have the Alpha's yet but will be purchasing this year, specifically for Home Theater. what I have found with my previous theater is that having the three front speakers the same makes a great deal of difference to the quality of teh sound they can produce.
With the Alpha's you have two choices. Do not use a center and have a smaller listening sweetspot in your room, if you rarely watch with a lot of other people and the room is not large this is an excellent option.
If your room is large (as mine will be) you should but 3 Alpha's and use a third Alpha as the center. Note that this will only work if you intend to use a sound transparent screen while you watch the movie.
The surround speakers are not as critical to the overall experience. However I would have liked to see a version of Danny's surround speakers using ribbon based speakers which would match more appropriately with the Alpha's.
So you may ask why am I buying Alpha's. Line arrays are quite simply the most dynamic type of speakers you can buy and that is what is required to gain any realism for both movies and music IMHO.