Despite not yet having the standoffs to mount the choke, I did install it in place of the first 270 ohm resistor, and simply set it behind the amp until the hardware arrives. Now, I'll admit to not really knowing how this is possible, but the choke definitely does improve the amp. Is it a gigantic improvement? Not really, but it is definitely noticeable.
The first thing I noticed is that bass notes are a bit deeper and more solid, yet not as forward in the soundstage. I can actually hear a bass note and its harmonics (or the strings vibrating, etc) rather than just a low tone or rumble, which is perhaps the biggest change. The bass actually is detailed and tuneful. Secondly, the soundstage has opened up a bit. Perhaps as a result, I noticed that things are a bit better balanced, in that the amp paradoxically seems less bright while revealing more tiny details in some songs (background noises, fingernails on strings, etc). Loud transients are now less startling and very smooth, almost effortless. The sound is even more natural than before. Finally, the leading edge of transients seems to be ever so slightly better defined, again without making the amp sound sharp or treble-heavy.
In short, a good upgrade, and likely my last! When an amp is so good that you forget you are wearing headphones, I don't know how much better things could get. This is definitely a "last 1%" type of upgrade, and to be honest, I didn't expect any difference with active plate loads following the power supply. I can only surmise that the choke is making their jobs easier....
