I had the same problem. I bought a Harman Magnum (used) because it was a good deal and because I heard good things about them. It was destined for the basement but numerous people I talked to said "oh, run the built-in duct to the upstairs, leave the basement door open, and the heat that builds up in the basement will in turn heat the floor, and you'll be good to go."
I have an A-frame with a vaulted ceiling, upstairs loft & bedroom. Downstairs there are two bedrooms. The stove is at the corner of the house that is below the living room, so the two downstairs bedrooms are at the opposite end of the house.
I started using the stove when it was not very cold out, just to get used to it. One night when it finally got into the 30's outside, my setup did not do a good enough job. The living room and upstairs bedroom, where me & the wife sleep, were fine -- there's a door to our bedroom that leads out to the loft and when that is open, the heat just pours in from the vaulted ceiling. However, the two downstairs bedrooms where the kids sleep were chilly. When I went in the basement it was downright toasty, which is useless because it is an unfinished basement.
So I set about a project not really knowing if it would work out. My ambition was to surround as much of the stove as I could in a "sleeve" and then duct that into the two downstairs bedrooms. I used flat sheets of duct sheet metal and then insulated the outside. The duct needed to be about 30' so I used insulated 6" flexible ducting. For fans I used two of those "duct booster" fans.
It's not pretty but damn if it doesn't work! It's not perfect, but those bedrooms do stay warm now. In fact, the smaller bedroom gets TOO warm if the door is closed. And the basement doesn't get hot anymore, but just warm enough so you can work down there, do laundry, etc. Whereas in previous winters it'd get uncomfortably chilly.
The one bad thing, however, is that that flexible ducting gives off an odor if the stove is running real hot. I measured the temps of the main duct and duct off my homemade sleeve. When the stove is at max, the main duct reads about 190' and the secondary duct reads about 170' which might be a tad too hot of the flexible stuff. Though I have noticed the odor less and less each time so I think the plastic is slowly "curing". My concern is it will eventually get brittle and crack.
As a final thought...I realize now, I really should have gotten a coal furnace, not a stove, but I didn't really know any better at the time.