I think you have just found out why the KZ's cost £40 and other in ears cost £00's.
The weakness in any IEM set up is the ear buds.
You need the best you can afford, they don't need to be custom molds but very minimum dual drivers but triple will give better separation. I use Westone as they are relatively inexpensive for the quality. Shure I have found underwelming personally.
Do not get the ACS in ear monitor converters. I have molded in-ear ACS ear plugs and bough the adapters - they were awful.
I can second what you wrote about the ACS. The driver thingy you put in the molded plugs sounds ass.. The ear plugs with the noise filter is great though.