You say you have 14" rough-in. Just to check, that means that if you take a tape measure and measure from the finished wall (not the baseboard) to the center of the closet bolts on each side of the existing toilet (or the center of the closet flange if you have no toilet in place), you get 14". Right?
Okay, so here's how the unifit works. The thing mounts on the floor over the flange and runs a pipe back towards the wall from the flange. There is a spigot molded into the portion of the toilet closest to the wall that inserts down (male) into the pipe on the unifit (female). So, I'll do a little diagram for you:
Flange---------------------------Xinsertion point for toilet
14" Unifit
Flange----------------------X
12" Unifit
Flange----------------X
10" Unifit
So...if you have a 14" rough-in, the wall is going to be further back from the flange so you want the rear of the toilet to connect further behind the flange. So you need to buy the 14" Unifit. The way it works, the toilet always comes with the 12" one, and every plumber who installs these has a zillion leftover ones, so they are essentially-worthless unless you want to sell it on ****. You just buy the 14" one and install it, and then mount the toilet on it.
Another way of looking at my diagram above is this:
WALL..X--------------Flange
10" rough-in
WALL..X-------------------Flange
12" rough-in
WALL..X---------------------------Flange
14" rough-in
Because the flange is further from the wall, you want the unifit with the longer pipe portion so you can put the toilet next to the wall and have the pipe reach forward to the 14" flange. Make sense?
You most likely don't need to actually move the supply line. Instead, your plumber can just do a 90 over from where it comes out of the wall so that it doesn't impinge the rear of the toilet. There is a little room between the rear of the base and the wall -- a little more than between the tank and the wall. It really depends upon your installation but it also might be possible just to replace the stop that's there with a 1/4 turn ball angle stop like a Dahl valve, and it may just fit. Dahl also makes a little kit especially for installing skirted Toto toilets.
http://www.dahlvalve.com/products/toto_toilet_kit.aspx
And here's the brochure for the same product:
http://www.dahlvalve.com/brochure/Totokit.pdf
Basically, it consists of a compression fitting that goes over the pipe coming out of the wall, and automatically has a built-in 90 followed by a quarter-turn angle stop with a small handle, so that it can fit essentially right against the wall. Look at the photo and tell me if that doesn't make sense. I guided a guy through it with videos and such a couple of months ago; he was freaking about having to call a plumber to install the toilet and when I showed him how easy it is for a laymen to install a compression angle stop on the wall pipe (remember to turn off the house water and drain it down before removing the old one), he just did it all himself -- got the Dahl kit, removed the old stop, cut the pipe back a bit, installed the new compression fitting Dahl kit, installed the toilet, and felt like a million bucks when it was done. I'll find the thread if you need it.
Good luck!!