I'm slightly taller and a little lighter than you, but we're close enough that my experience should be relatively similar. Also, you should know up front that I'm a mountain rep for Head so my opinions are suspect.
I've skied the 177cm SS Magnum as my "less than 6" of new snow" daily ski for the past two winters. I think it's an incredibly versatile ski that works fantastically all over the mountain. It DOES sink in deeper powder, but I think that's essentially a given for almost any ski with a 71mm waist. It's probably SLIGHTLY more prone to sinking in deeper snow than models of similar width that are a lot softer in flex, but softer skis give up a lot of the hard-snow performance that makes the Magnum such a great ski. I probably skied the Magnums more than 130 days during the last two winters, all but a few of those days were here at Jackson Hole. I think it's just a great all-around ski when the snow is boot-top depth or less. (And it's not THAT bad in deeper snow but nobody wants to hear that.)
With all that said, I've just spent the last two days skiing a new pair of i.Titans, also in the 177cm length. The Titan will be my "daily" ski this season, partly because the shop I'm affiliated with is carrying the Titan this winter and not the Magnum. I've now skied about 40,000 vertical feet on the Titans in a whole bunch of different conditions (pretty firm groomers, trees, chalky steeps, moderate bumps, 5" of powder, and lots of cut-up stuff). I'm super happy with the ski. It's got the same strong, smooth, glued-to-the-snow feel of the Magnum with just a bit more width at 79mm underfoot (in the 177 length) versus 71mm for the Magnum. I'm finding the Titan to be really nimble despite the additional width. I honestly don't know that I can feel a "huge" difference in flotation, but the Titan seems to ski very, very nicely in the moderate powder and crud I was in today. I know speed isn't all that important to you, but this ski was outstanding at some pretty high speeds yesterday - so much so that I frostbit both cheeks.
My own philosophy about skis is that I'd much rather ski moderate powder on a "narrow" ski than ski groomed or packed-out/tracked-out snow on a "wide" ski. For me, the performance and responsiveness of a "frontside carver" is so much more exhilarating if I'm skiing a few inches of snow or less that I really, really prefer that kind of ski for those days with no significant new snow. Even here at Jackson Hole, there are usually about 50 days a season (or more) that fall in that category. That's why, for me, a ski like the Magnum or the Titan makes the perfect "front" half of a two-ski quiver.
I think you could be very happy (ecstatic, even) with either the Magnum or the Titan, but the Titan might give you a tiny bit more versatility in soft and new snow without giving up much of anything on hard snow.
Good luck with the choice.