How are you setting up Vandersteen 2c pair in a restaurant setting to get proper fill to most patrons? It may be a high value, good stereo speaker for home use, but I doubt it's going to be an optimal solution for your purpose with just a single pair. The SPL at one end of the room is going to be much higher than the other.
Probably a better solution, is to use a high quality 2 way monitor such as Behringer B2030P, about 6-8 units, placed around the restaurant, distributed evenly down the length of the central area for more uniform sound. These have extraordinary fidelity for the price, and dispersion is extremely wide, making it suitable. The price is very deceptive here ; comparable 'hifi' speakers cost several times the amount(and this is based on objective comparison of construction/parts/actual measured performance). You need to combine these with an active 2 way crossover (Behringer CX2310 is fine) and 4 or more small subs such as the Dayton 10" powered units (add pillow in each sub - seriously - this will give perceived tight bass effect from each one ). But it will be much easier to integrate the small speakers recommended above. I recommend mounting close to ceiling using angle mount pointed down toward main field of listeners. Use a high bandwidth/broadband acoustic absorber behind and above each speaker for optimal SQ. Place the subs using the same distribution, along the walls. This will allow a minimally obtrusive, extreme high fidelity(for this kind of setting) solution.There is at least one other here that followed this setup, and had spectacular results(he used more expensive subs and a more powerful xover, however).
If you insist on the Vandies, I highly recommend getting 2 more pair, and distributing them along the room in the same manner as to provide more even sound to the patrons.
-Chris