The ZTac dual comm PTT works very well (
here is a review of the Z118 Z4Ops. I've used one with two Px-888s with no troubles. I did find that the ZTac unit works best without a battery inserted. All the battery gives you is volume control via the PTT, but it also adds a lot of noise to the signal. Hence I've always used the thing in unpowered mode.
A friend sent his ZTac dual comm PTT to SRS Tactical and had it re-wired to work with real single comm Sordins. He has reported that this setup works very well with his dual Px-888s.