external DAC with SACD

Please excuse what may be a stupid question, but here goes. I've got a Marantz SA8005 CD/SACD player, and a PS Audio UltraLink DAC through which I play Red Book CDs, using the Marantz as a transport. However, SACDs will not play through the external DAC (I have the Marantz connected to the CD input on my amp, routed through the PS Audio DAC, for Red Book CDs, and to the Tape1 input, in order to bypass the PS Audio DAC, to play SACDs). I read somewhere that SACDs have some sort of encoding that prevents this, but that there is a way around it.

I ask because the PS Audio DAC very definitely improves the sound of Red Book CDs played on the Marantz (I can, of course, A/B Red Book CDs through either DAC by simply pressing the Tape1 button on the amp's remote). I can only suppose that playing SACDs through the PS Audio DAC will improve their sound as well. In fact, a standard Red Book CD played through the PS Audio DAC is, in some ways, better sounding than the same recording on SACD played through the Marantz's own DAC. For example, I have compared the DGG CD of "Credo"--a Helene Grimaud recital featuring, among a variety of other things, the Beethoven "Choral Fantasy"--against the DGG SACD of the same recording, physically changing discs and engaging the Tape1 circuit for the SACD; allowing for subjective uncertainties introduced by the necessary time lag, and the possibly different mastering of the two discs, I still believe there are aspects of the Red Book version through the external DAC that I prefer to the SACD through the Marantz, although I do think the resolution of the SACD is marginally better. 

Thanks in advance for your sage advice.