Jafox,
Correct me if I am wrong, but isn't the LS-5 the preamp that only had balanced inputs and outputs? Therefore, if you are not running balanced cables, you will need to buy them, and if your equipment is not setup to run balanced, you will have to replace that as well.
From my research into ARC preamps (and I own an older LS-2), I have formed the following opinions:
A.) The LS-16 is a good preamp, but not a whole lot better than the other LS series preamps before it, (and not much worse than the subsequent LS-22). (With one exception: The LS-5 which was reputed to be very good.)
B.) The LS-25, Mk II is a very good preamp. This will sound about as good as the LS-5, but it has more bells and whistles.
C.) The Reference II (Not the original Reference though, which was a glorified LS-25), supposedly sounds better than all the previous ARC preamps. (I have a friend with this preamp, and combined with his Avalon Eidolons and his 400W/ch Classe amp, it produces the finest sound I have ever heard from a stereo system.)
BTW, my choice, when I get the cash, someday, will be to upgrade to an used LS-25, Mk II. I want to have the sound of the LS-5, with the bells and whistles of a modern design, without having to take out a second mortgage on the house! (Plus the option of not having to run balanced inputs. I run balanced out, but my phono preamp, and my other equipment is just not setup to run balanced cables unfortunately.)
These are my opinions, so don't start a flame war.
Good Luck in your search!