I saw these 50% off open box so picked them up on a whim for $9... they sounded like a really bad Beats knockoff. Bass was boomy and spilled all over the place which overpowered the already weak mids and highs. I was going to salvage the asymmetrical pads, and send the rest to the junk heap. Then I decided to tune them myself.
After looking at some RX700 and 900 mods here's what I came up with:
Three pieces of tape per side. In my case I used some cloth tape to:
1. Cover two of four holes in the metal backing of the driver. This copies the same tape config on the stock RX700. (middle tape in the picture)
2. Cover two of five "passives" on the driver mounting plate. This reduces them to the same number as on the RX700 which is 3 (right tape in the pic).
3. Seal off the port in the housing (left piece of tape). Probably just a good idea.
To me, this tames the bass a lot and allows the mids and treble to come out and be decent. If I had more time I'd experiment with the number of holes covered, but as I don't expect ATH-M50 performance out of these things, I'm happy leaving it as it is and now using it as a general-purpose set of headphones.
The usual stuffing of the pads brings the driver a little farther from your ear (it was touching mine on one side). Whether there is a soundstage improvement is hard to say.
If anyone out there has more time, or maybe also has the RX500, 700, or 900, it'd be interesting to hear your mod stories on these little guys.