You should be able to get a nice sound out of a Martin D16.

If you are micing the guitar or using an acoustic amp, you can get into a lot of trouble getting a good sound no matter what strings/guitar.

I haven't used SP strings so can't comment on that. I use Thomastik strings and I like them:

http://www.guitarcenter.com/Thomastik-SB211-Spectrum-Bronze-Light-12-String-Acoustic-Guitar-Strings-101399-i1122678.gc

I don't find the sound too bright at all.