I also have Sanger V215. I have 4 in the cabin also - the front 2 are same as Ryans (very good location IMO). But, my rear two are on the right and left side toward the back (just to the left and right of the arrows Ryan drew). Mine came that way. I am glad they are on the right and left - took a big wave over the bow last summer - huge wave into the boat. Water puddled up in rear against back seat (right where Ryans speakers are). Took a minute or so for the water to seep into the bilge. I hope that doesnt happen again, but my speakers were safe...
Ian - I have complete pics of my whole system install if you are interested. I put the whole system up under the drivers dash - completely out of the way. No loss of storage. Let me know if you're interested - PM me with your email and I'll get you some pics of what I did. I fit a 10" alpine sub up under there too :-)