Thanks Jeff,
I'm waiting on the passive couplers to arrive and then I'll go from there.
Actually, believe it or not, I have had very few problems switching x10 stuff on and off from either bulding to the other building.
Once in a while I get a stray light coming on or off by iteslf.
I have a ton of signal suckers here.
I have a cat6 network spread between the two buildings with a total of 4 large UPS battery backups, 3 PC's, TV's, battery chargers, all the usual suspects.
The cm15a X10 USB transmitter is not even close to the house sub panel, it's all the way at one end of the house and it is on the protected side of a large UPS right next to the computer.
Not sure how it is all running so well but it could be better I am sure.
By the way, the exterior main breaker panel I show in the diagram above has only big 240v breakers in it for the AC, Heat pump, both sub panels and the electric range.
The 240v water heater, well pump and clothes dryer are on the house sub panel.