Line Filter Question

I'm posting this in two areas as I'm not exactly sure where it fits. I have been using a Monster 3500 line conditioner and am less than impressed. I live in a condo that is bulit like apartments leading to a good deal of interference. What filter do you folks recommend for my cary/belles tube/ Merlin vsm system? I will be buying second hand.

Thanks in advance
None on the amp - it should be plugged directly into the wall. Use the existing line filter for the digital source only.
If an Isoclean falls within your budget, I'd recomend one wholeheratedly. I'm using a 60A3 in my system, and even in a single family dwelling with a dedicated line for the rig it helps. It feeds my Tom Evans or Audion amp, the TEAD Vibe preamp, and Audio Note DAC and transport. I leave the subs plugged straight into the wall, because I haven't heard any benefit from filtering them. Isoclean is pricey, but it's the only one I've heard that didn't bring any sonic compromises to the table.

You still get the buzz from your Belles?
Can you have the system in an separate circuit?
IF power basics are covered the filter might well be the icing on the cake for getting the most out of your system.
Please your comments
i have used the ps audio ultimate outlet with both amp and source components. if you use the 20 amp version, you should be ok with most amps.