According to this file
, the Digital Stream DTX 9950 uses NEC1 device 18.52. The 15-2116 can't send this device.subdevice combination, nor can it be manually modified to do it.
For UEI remotes, the setup code Cable 2303. The RCA RCRP05B has this setup code, and will definitely work. I suppose that cheaper remotes like the RCA RCR503BR
will work, since it has setup code 2303, and the code list says that is for Digital Stream.