I returned my DSP A-1 for the RX-V1 in order to get the benefit of the 92KHZ Dacswhich I feed a true digital 96/48 from my Denon 5000 DVD player. That being said, most of the new formats (i.e. Sonys SACD and the DVDA) are only outputting an analog signal. Which means that the DSP A-1 will do fine with these newer formats by utilizing the 6.1 channel analog inputsthese bypass all DSP functions and, or course, circuitry.
IF you happen to have a device that outputs a digital 48/92khz signal, then the older DSP-A-1 would miss out on this higher sampling rate material. But remember, if your external device has good dacsor if you purchase a good outboard dac such as MSB technologies, you would never need to upgrade for this reason alone.
As for the DSP modes on the YamahaGod if I havent heard this argument beforeIf you have the Entertainment dsp on your Yamaha you can alter it to deliver 8.1 channels of stereo. Of course these are not discrete channels because the music was not recorded in 8.1 discrete channels. But it will fill the room nicely with soundjust as the Denon will do. Yamaha decided they too were sick of hearing about Denons 5 channel stereo so on their newer and less expensive RXV1000 they re-named one of their DSPs stereo. Its all in the delivery I guess.