Advice regarding separate DAC purchase

The Pontus is not a lateral move but, given the investment level you spent on the integrated, something in the $4-$5k range will likely serve you better.  If that is not economically feasible the Pontus is definitely several steps up from the DAC1 that comes with the 8900 and is worth the cost imho.  You can always give the Pontus a spin as you can find them used.  If you don’t like it it’s not hard to sell them as they are well liked.  Places like The Music Room have a 30 or 60 day return policy as well which would give you plenty of time to determine if it works for you or not.

One last thing, the DAC1 module is a decent DAC and, if you don’t want to spend money on a new one, is more than capable.  Streaming is a fantastic way to listen to and discover new music.

The DAC1 module in Mac gear doesn’t have a great reputation and several here have replaced it with a separate DAC and been very happy with the improvements.  I’d recommend getting the Pontus ll along with either the Iris or Hermes DDC and use the i2S connection that provides a big sonic upgrade.  You won’t be disappointed.

Seems there's a consensus among you that this may be closer to a lateral move 

as others have said... don't think this is correct ...

but whether it is worth the op's while given his overall system, i dunno