I have an RX-V1400 (almost identical to the 2400), and I also prefer straight stereo mode on some stereo material. However on others I like 7-channel stereo mode, which is theoretically very artificial but it sure sounds good. On other material PLII sounds best.

Try some of the material Dolby recommends for evaluating PLII, and see how PLII vs stereo works for that: http://www.dolby.com/tech/co.br.0102.PLIIDemo.pdf