Does that mean we cant use aftermarket cables bought from other places?
Well, there's a few answers to this.
Officially, no. But some others on here have found off-the-shelf cables that still fit without causing any damage.
Another one or two have got some cable and made their own!
Finally, it also depends which IEM you're referring to.
For the current edition of the PM4, see above.
The upcoming PM6 and Hunter will be available (to those that want it) with the normal industry standard 2-pin connector.
And the proposed and upgraded new PM4, Sabre, PM6 and Hunter models (Mk II, if you like) will have a completely proprietary solution, with cables permanently fixed to the IEM's and terminating at the Y-spilt (where a variety of different cables/modules can be attached). That's all here on this thread if you want to read more.