I have the RT-1 with the original cable, I have the TRN silver up-grade cable and I have the Silver KZ up-grade cable for the ZST. I just tested all these with the RT-1 and I couldn't notice any difference in the sound. The original cable didn't work for me because it was so springy that every time I moved I lost the seal in my left ear. The TRN cable is very nice and has formed ear guides without a wire. For some reason I continued having an issue with the seal in my left ear. I saw Auglamour's new F100 which looks to be the same shape without a removable cable and it shows it being worn cable down. The KZ cable I have is one of the originals that didn't have the wire ear guides and I had trimmed it down to work with the KZ ZS. What I found worked really well for me was using this KZ cable switching the Left and Right earphones and wearing them cable down. This provided me with a better fit in my left ear so that I didn't have to keep repositioning to keep the seal. I might be wrong and if so I'm sure I will be corrected but I don't think the +/- matters as long as it is the same for both earphones. They are either in phase (both the same) or out of phase (one is different than the other).
Thanks for this reply even though I am confused more than ever about this. Either you've been listening with wrong polarity all this time or I am crazy... I have 2 pairs of those small cables that go to the bluetooth module, one pair is RT-1 2 pin and other pair is regular 2 pin cable. Here is the thing, I just reconfirmed my findings, regular 2 pin connector compared to RT-1's has one side different in terms of polarity. I also did confirm this by listening to polarity tests online and for me only one question remains - which side of RT-1 is different compared to other IEMs. The regular 2 pin cables for bluetooth don't have a clear indication how they go into IEMs, they have L and R marks on the silver part but on the connectors there is only a small circular hole on one side of the connector - if I assume that that hole is supposed to go towards the head then left side of RT-1 is inverted and ground goes back while signal is towards the front.
You have all the tools to make a definitive conclusion, you just have to check the original RT-1 cable compared to KZ or TRN cables. Test closed circuits and see what part of the 3.5mm jack is connected to which pin on cables - if you have no experience, tip of the 3.5mm jack is L+, second part is R+ and last metal part is common ground R- and L- (having one more metal part would be for the microphone if any of the cables has it). I didn't have voltmeter so I tested it with a battery and a TV remote, you could use a small LED or anything that will show you whether the circuit is closed or not.