OK my $0.02.
I am a believer in amplifier/coupler such as the ACT CR 234. I have had Leviton/X10 repeaters and had DIM / BRI problems. I have owned or tested three ACT units and they all handled DIM / BRI correctly.
More signal is always better, especially if you have signal suckers and noise generators (and you do whether you know it or not). If my current ACT units fails, rather than fixing I will use the excuse to by Jeff V's, XTB II. I have seen nothiung but good reviews and praise for this unit.
Yes - I should have mentioned my problem was with a Leviton repeater (HCA02-10E) - the ACT has a MUCH better reputation (but is more expensive).
idbl:
1st -To save money I would try a passive coupler first: This is the one I use (I think)
http://www.smarthome.com/4816h.htmlOf course, there are plug in ones - don't forget you can save a lot of money on X10 stuff on eBay.
2nd - if that doesn't work, I agree with Dave and would try the XTB. Probably able to return if it doesn't solve your problem. Check w/ Jeff. (On the original and still cheaper version of the XTB, it would help to already have a coupler. Quoting Jeff's page: The plug-in XTB is certainly the easiest to use, but it should be paired with a good passive signal coupler for most installations)
3rd. If the above fails, get the ACT and ONLY the ACT.
But if 1 and 2 don't work - I think you have other problems - ie NOISE.
George