I have great luck with streamers, but not necessarily tandems. It depends on the day / time of year whether you want to go with a single hook streamer or a larger/longer tandem hook streamer. Generally I have better luck with single hook streamers in sizes #4 and #6. I've had success fishing them with lead core, sinking fly line, and off the downriggers. I generally do not use a dodger/flasher unless absolutely nothing else is working as I like fighting the fish with a less metal in-line as possible. Generally haven't had great luck with them either...not sure why. I experiment on speed and have run them anywhere from 1.5 to 3 MPH but generally start out at 2.5 MPH or so. Of course adjusting speeding and doing S curves is always a good idea (or a jigging machine).
on leadcore, my favorite set up is a meduium/large dodger 15 inches to a fly........always get at least a fish in a 3 hr trip. been using this combo for 20 years.