I don't use the EPL, but I have the remote option with a mute button which I use quite a bit (given the limited time I've owned mine). I've messed around with the tone controls a tad, but I wouldn't say I use them in any practical situation, just simply testing out the new ride. I haven't messed with the stereo/mono or the filter yet, although I might try the stereo/mono thing today. I use the low gain switch quite a bit, because paired with a double 440, I can't turn the knob very much before the volume is way loud. I'm not sure if leaving low gain on all the time is a bad thing or messes with the sound quality at all. My guess is no.
One thing I'd like to figure out is how to listen to my headphones without the speakers also playing at the same time. I grabbed my Grado's yesterday figuring I'd check out that feature, but I couldn't figure out how to make the speakers quiet while keeping headphone sound, they are either both on or off. On some of my other gear, its an auto mute for the speakers when phones are detected.