My son is putting together an HT, a realm I know little of. He has Cornwall II for the fronts, Heresy I for rears. I get the idea that the center is all-important for clarity of dialog and such. I was thinking either a Cormwall on its side used as a stand for the flat screen or perhaps a LaScala used as a stand.

Another question...will the magnet structures of either of these mess with the picture? If so, how does one ameliorate the effect?

As you probably know, there is a "vertical Cornwall" available from time-to-time on the used market, but they're not available new anymore.  I supposed you could make a vertical Cornwall by replacing the front face of an older Cornwall with the vertical configuration, but this might be challenging if you are not a woodworker.  I'm sure that someone on this forum could give you dimensions of the driver locations in the vertical Cornwall.

A secondary choice, but still very desirable, would be a Heresy mounted on the floor, i.e., not on a stand or above the TV. I would also recommend a Heresy I (HI) over a HII, but the HIII is probably preferred to the HI.  

I think the answer to your second question is - potentially a problem for a CRT-based TV of large dimensions.  Probably not as much of an issue with flat panel LCDs.  The way I would deal with the problem would be to shield all the connections to the center speaker's drivers, and add a bit more ferromagnetic material (like iron and steel) around the magnet structure to capture some of the stray fields.  I'm sure that a Google search will turn up multiple ways to do this.

Chris

I am pretty sure LCD and plasma's don't have issue with magnets, I have put alot of speakers close to flatscreens and never seen any fluctions.

I know a few people that needed the mag sheild have found them, I forget what they are called.

If an extra CW can be aquired that is the way to go, either hoz. or modded to vert.

Definitely use a Cornwall or at least the Heresey. The center channel is one of.. if not the  most important piece of the HT puzzle. Don't have room?? change stuff around. The last place you want to cut corners.