DAC - Aqua Formula or Aqua La Scala

https://www.stereophile.com/content/anthem-electronics-str-da-integrated-amplifier-measurements

If the DAC in the STR preamp is similar to better to the one in the STR integrated, I highly doubt you will get an audible improvement regardless of DAC. If you use ARC, then you are digitizing the analog inputs anyway, so now the ADC and DAC are active, on top of the external DAC, so that’s a lot of THD, IMD, channel separation, etc. that gets compounded through each stage, not to mention the analog inputs themselves aren’t ultra clean. You may make the sound different, but I highly doubt you will make it cleaner; and if you wanted different, just mess with ARC.

Agreed.    Reintroducing the output of either Aqua DAC into the digital domain in a budget piece like the Anthem is a bad idea.  I've heard the Formula.  It's among the smoothest and most analog sounding DACs to be had.  If you can afford it, then upgrade to a better preamp. 

You can't go wrong with either of the AQUA DACs, Formula is better (more neutral) LaScala very slightly burnished with tube rolling ability.

Worth waiting for the ARC Genesis release before changing??

Talk to Tony at Ellington HiFi. He carries Innuos and Aqua and is that rare bird, an honest and no bullshit audio dealer!