So, I have ordered S earpiece adapters from Awwan, a replacement Westone cable, and a TRRS plug. I'll cut off the TRS plug and solder the TRRS in place of it. Total spent was approx. $60. Hopefully it turns out to be a nice upgrade with the HM-901 and Bal card Worst case scenario is that I'm sure someone would love to get some of these adapters 2nd hand, and a Westone user would appreciate a TRRS cable.
I was able to sell my adapters and UE cable very quickly after I decided they weren't for me. Looking forward to seeing your finished cable. I'm always on the lookout for ER4 mods.
Vwinter you're using red filters yes? I get a dip around 7k in comparison to 1k, but no dips below 1k until bass starts decreasing at 50Hz. Was doing the MH1 for a while, but I'm back on the ER4S now. This kind of clarity is so rare imo. Been lovin me some Dream Theater.
Also H20, I'm finding the UHA760 to sound wonderfully flat with the ER4S. It does seem to put out less power than the UHA-6S.mkII. I sometimes go up to 50% volume on the highest gain with some quieter songs. I do listen a bit loud at the gym though. But really I find it quite transparent.