Ive done 2 or 3 powder runs on the Bowls at Breckenridge and I was starting to get some bad leg burn. it seemed like the tip sank a little bit if i wasn't leaning back a lot. maybe i just need more time on the back slopes?
This is generally going to be true of most twinish center stance boards. I'm told there are exceptions... but most of those are powder specific twin board... which for you case it pretty much that same as dedicated powder board in that you would have to buy another board.
Setting your stance back a notch or two is really going to help (but you are still going to get some leg burn). Try sportslegs