what speakers do the best "disappearing act"??

I have a pair of Sonus Faber Extremas and are as transparent as they come. I know I will get told I am nuts for this but properly set up they will actually image behind you at times.

yes the avalons are very good . try jm lab . sound labs with tubes are scary. that is what you are looking for i think. tim why dont you go hear the labs with good tubes?

I agree with Redkiwi. You need to find help in setting up your system. I can only add that analog (records) do it better than digital.

I've always felt the same way, that alot of speakers don't completely disappear, at least my limited experience. I've always considered my listening rooms less than ideal even with acoustic treatment. But aside from the significant effects positioning can do to acheive your goal, good electronics are also important. A better piece of gear can have a way of really getting the sound "out of the box." Another thing I wonder is how significant it is for the driver to be the only thing vibrating in the area, i.e. cabinet resonces may be to blame for messing up an otherwise capable driver for the task, among other things.

My tops are avalon eidolons and audio physics (virgo, avanti, spark and tempo ). The virgo is in a class all it's own for the 2500-2800 range.
A Tube preamp/amp will generally increase a sense of presence as well. Moving the speakers out into the room, and clearing away /covering reflective items helps too.