This might me a little late but that Red Star Cuvee potentially could get up to 18% ABV. Since you want a sparkling mead you could stabilize it, back sweeten and then force carb it in a keg or ad more sugar to hit close to that 18% with some sugar left over.
I would recommend using the mead calculator at www.gotmead.com
to figure out what you want your end gravity to be and what you need to mix in to get there. it's going to be a little tricky to calculate but I think if you use the originally SG in calculations you can get the right numbers.
I'm going through this now trying to figure out the best way to dilute a csyer that is near the upper end of the yeasts alcohol tolerance but still too sweet for my tastes.