Here's my take on things. I should state that I have no experience with the FIM or the Acme, but in the past year and a half I have experimented with about 5 or 6 sub $20 receptacles, with it being pretty apparent to me that there are some pretty big differences in sound quality, and that is with a system that probably costs about 25% of what yours does (maybe less).
I would doubt that the overall character of the FIM is going to change that much for you. My experience is that receptacles will give you almost as much difference in sound as power cords will. They may also, like power cords, be system dependent and I'll get to that in a minute. My experience is also that if you are running multiple receptacles within your system that you can best judge the "sound" of the receptacle only if you run all FIM, all Acme, all Hubbell etc. In other words, if your system is drawing from more than one receptacle (like most are) you better not mix and match if you really want to establish the true sonic character of the receptacle. All of my conclusions are based on using the same receptacle at any given time, throughout my system (ie. at the wall and in my line conditioner as well).
I had originally been running orange Levitons, and have experimented with the P&S 5262 (better than the Levitons), the Arrow Hart 8200 (better than the P&S), and the Hubbell 8200 and 8300 (better than the Arrow Harts-I changed my mind on this recently after some further experimentation). All of the above "better thans" should be followed by "in my system", which is solid state based and leans toward the brighter side of neutral. As Craig's recent post on the FIM outlined, from his perspective the FIM presents a "darker, mellower, richer" sound in his (also solid state) system. In my system the Hubbells (which I currently use) do this, although I think they actually do more in terms of eliminating "distortions" which the P&S and Arrow Hart introduce. Putting the Levitons (the worst) aside, in my system, the P&S 5262 was the "brightest" and most forward of the bunch. The Acme is a tricked up P&S 5242, so it doesn't surprise me that it is more "detailed", or appears to be at initial listen, than the FIM. I bet it is. The character of the P&S that I used was definitely "front row" as compared to the Arrow Hart which was a bit more "mid hall" or the Hubbell which is possibly even more "mid hall" or further. I've had e-mail correspondence with Dekay about this, and in my system the P&S, although better than the Levitons and initially impressive, totally fell apart when compared with the other receptacles. The Arrow Hart had a beautiful, very open mid-band, but was definitely more forward than the Hubbells and ragged at the frequency extremes compared to the Hubbells. The Hubbells have an extremely "black background" but for some tastes might be a little dark. With a tube set-up, though, it might not be the way to go. Maybe it is a ditto for the FIM.
All I can tell you is that, in my system, the smoother sounding receptacle is, in my opinion, the most accurate, although it may not initially be the most exciting. All the detail is there upon careful listening, although it is presented in a different (I would call it a smoother and more refined) manner. But the "perfect sound" is a pretty subjective matter and what may appeal to you (detail, forwardness, etc) may not appeal to me (a preference for a richer, mellower sound with a more mid hall perspective). Then you have to introduce tubes versus solid state issue and their interaction with the receptacles, so what is effective in one system may not be in another. I think receptacles may just be another example of this.
