How can a PS Audio Perfect Wave DAC enhance my system?

It connects either way unlike your claim of getting DSD out of that Marantz. Notion? Sounds like you're in the wrong hobby.

I ran my my PSA DAC with a Sony UBP-X1000ES with a Chinese HDMI to HDMI I2S adapter so it would decode the SACD Layer of any disc or DSD file.

Fuzztone, thank you for your stellar contribution to this thread. 

1) the PS Audio DAC can be used with CDs, SACDs, and other digital sources.

2) many DACs can be used as digital preamps, because they supply enough gain to amplify the original signal of a digital source.  I owned a DAC like that and definitely preferred the sound with the preamp still in the system.  These DACs are not designed as pre amps and therefore tend not to sound as good as having a traditional pre amp in the system, but ymmv.

  As per my first post in this thread, I suggest you attempt to audition the DAC in your own system and let your ears decide.  There is an element of subjectivity in this hobby 

Thankyou mahler123.  I feel more comfortable not having to discard my McIntosh preamp.  Just trying to  understand the I2S as this is new to me.  I have the opportunity to buy the PSA DAC so that would be an expensive way to audition if it is as subjective as you suggest.