Marantz sa11 S2 - upgrade to outboard DAC?

What don't you like about the Sa 11- S2? Fairly well respected unit that plays cd's & SACD's very nicely. 

it is nice.  just was wondering if there are any upgrades that would make it even better.

I have the SA15S2b SACD player and some friend brought over a couple of DACs and I even tried a Schiit Bifrost (a step down?) and it always seemed like a sideways move, at best. 

Going with a better PC (TWL Digital American), better fuses (no need to overspend as there are 4) and upgrading speaker cables (Cabledyne Virtuoso) and eventually getting a better integrated (Kinki EX-M1) made it very clear that the Marantz was outputting great digital all along. All that was needed was for the rest of my system to catch up. 👍

All the best,
Nonoise