[paolo]

Well I DO have a VOIP system off my cable modem, I mistakenly amp'd my modem drop by mistake. All I can tell you is that I've had success just leaving the drop alone.
The problems I was having with my voip were due to the crappy SMC modem that Rogers gave me, once I changed it to the Scientific Atlantic modem and they all went away. Like I said before, and I'll say it again, since you have the amp, just give it a try with and without. cant hurt. You dont have to take my advice, but try it with and without the amp and let us know how it goes. Good luck with this!

p.s. noticed you said you have good signal at your demarcation point, why not just put your modem right off the leg at the demarcation as close as possible, therefor it will have little to no loss? then once its converted to ethernet, you wont have to worry about loss over distance, because ethernet has different you can even put your voip adapter right off the modem as close as you can?

P.P.S. I never heard about if your signal back to Rogers is weak, their system automatically throttles your down/upload speed and conversely, a strong signal causes their system to increase speeds?. I DO know that it is roger's responsibility to ensure your modem get strong signal, and if it doesnt they will replace what ever necessary until your modem does.