In case anybody else is interested, I now have Trantec hand microphones on all four of the new frequencies of 173.8, 174.2, 174.6 and 175 MHz. With all receivers close to the mixer and testing each microphone within 3 feet of the rx, I can use any combination of two and the two combinations of three excluding 173.8, 174.2 and 174.6. Obviously I cannot use all four together. Interestingly, even though the combinations above are useable, an output from intermodulation can always be seen on the unused channel when other combinations are in use. I will experiment again with increased distance between tx and rx and add to this thread. I only have two VHF belt packs so cannot test these where the results may well be different because of the increased power.