After two years of messing with X10- I got it reliable.
here are my suggestoins for what it is worth
If you want motion sensing room lights... buy them from HomeDepot (Heath, Leviton, whatever)
If you want porch lights on at dusk and off at dawn- buy a timer from Lowes that auto adjusts for sun times... mounts in the wall in place of normal light switch.
For actuall X10 reliabiliy-- Get the XTB II R for phase coupling
http://jvde.us/xtb/xtb_reports.htmDon't even mess with anything else (I did).
For RF reliablility get this:
http://www.wgldesigns.com/v572.htmland plug it into the XTBR -- you can get the V572A (the one without the power line interface) if you have the XTBIIR and will blug the transciever into it directly through the little cable.
Dont mess around with trying to mod the range of the X10 transcievers or add multiple transcievers or other phase couplers etc.
If I would have done the above.... earlier... life would have been better.
These are just my thoughts... that is all- your mileage may vary.
Enjoy!!