When DSD Remastering is on, the audio is already being played as DSD 5.6 MHz (for the DMP-Z1) or 11.2 MHz (for WM1M2), so we know that Direct Source doesn't exactly apply to DSD audio (as DSD is being played-back natively), so in the case of the DMP-Z1 how could Direct Source be combined with DSD Remastering? Also, if Direct Source is not on, then we can see the effects screen, even if they wouldn't work with DSD playback (similar to how we see the effects screen when we use BT to listen to some BT headphones, even though effects are not working).
I would say that for the DMP-Z1 they just didn't want to do too much work to change the UI, so they just added DSD Remastering to the Walkman OS and then forced us to have Direct Source enabled. In this way, the effects screen is not displayed (so we won't think that effects might be usable).
What I mean to say is that even on the DMP-Z1 it was always a case of Direct Source OR DSD Remastering OR Sound effects, and not Direct Source + DSD Remastering.