I have not heard of the Hughes DVHS HDTV recorder. This is a section for HDTV Recorders so I assumed you have a HDTV DVHS recorder. The Panasonic DST50/51 accepts only an 8VSB RF signal on it's input. Your DSS Hughes tuner would neet to output an 8VSB RF signal to feed the DST5x tuner. This tuner is designed to output a 1394 firewire signal that carries an MPEG2 video digital signal. This is not the same as the firewire signal used by minidv camcorders which is a "native DV" video signal. Therefore, you cannot simply connect a firewire between just any i-link connector and the Panasonic tuner or Panasonic DVHS VCR. Not all 1394 I/O's are compatible.
You have two, possibly 3 options.
1. Locate what is called the "Panny combo" which consists of a
-DST-5x tuner (you already have)
-DishNetwork5000 with HDTV modulator
-Depending on your current dolby decoder you may need a Techniques SAHC500 dolby decoder for full dolby compatibility.
-subscribe to DishNetwork HDTV channels
(This is the only currently reliable way to record and playback the HDTV movie channels and OTA HDTV sources)
2. Contact 169Time and inquire about getting a DTC-100 modification to record to your particular DVHS recorder. Their product is still under development but they are reported to be shipping partially working retrofits now.
3. If your Hughes dvhs recorder has a channel 3 output you could connect it to the channel 3 input of the DST5x but I don't see what purpose this would serve for you.