We use an Exact Power EP-15A to maintain level voltage, much as Jsmoller does. Isolation devices beneath that make a clearly audible difference (improvement) in our system.
I suspect this is because the EP contains a large transformer. Every device in our system that contains transformers benefits from vibration management. We use cryoed Symposium Rollerblocks with tungsten carbide balls and they work really well for us (and yes, we've A/B'd and hear the difference between non-cryoed/cryoed and stainless steel/tungsten carbide.)
Whether isolation would benefit a pure power "conditioner" (whatever that is) I can't say. Stringeen says emphatically no, and advises losing the conditioner too. :-) OTOH, I've heard improvements from reducing vibrations in "just pieces of wire and electonics" - a hundred times. FWIW I've done the test he suggests with our EP, quite recently in fact. It's not going up for sale. Don't know about the Monster, never heard one.
Sol322's advice to try it and decide for yourself makes the most sense to me. You don't need us telling you what you can/can't hear! :-)