Earl,
How about a link to the Summa's you mentioned. The A7's I am already familiar with as I cut my teeth into high efficiency with them and then moved on to JBL with mainly my variations of the 4 Pi Pro system Wayne came up with.I use (Bruce) Edgar wood horns with Altec 902's for most of mine though.
By the way, Colin is using stock N-501 8A crossovers which could be improved on.
Regards, Ron