unicast UDP stream not working

We’re having an issue with the EMS (a perpetual license we’ve purchased from you) that I hope you can help us with… We’re using the EMS to take in a unicast UDP stream (dynamically created) to make it available for RTSP streaming. With VLC this works fine, but when I use the device this is intended to work with (a STB), it doesn’t work… Doing a tcpdump, we’ve tracked the issue down to the form of the RTSP SETUP command. With VLC, there’s a RTSP OPTION, then a RTSP DESCRIBE (where the audio and video channel are identified as track 1 and track 2, respectively), and then the RTSP SETUP url is something like: rtsp://ems_ip:rtsp_port/1234-abcd-3221-efa0/trackID=1. With the STB, the URL is rtsp://ems_ip:rtsp_port/1234-abcd-3221-efa0, which results in a "Invalid track" error. My question is, is there any way to bypass this test and just send the video through RTSP? There’s only one audio and one video stream, so the STB will choose the right ones… This happens with two target STBs (different vendors), and we can’t modify the inner workings of their RTSP player.