I haven’t heard it personally but my dCS dealer told me that Apex upgrade was substantial and worth pursuing. I honestly don’t care for dCS as a brand, firstly its house sound and their policies for 2nd hand customers (upgrades and warranty).
I feel very fortunate to invest in a DAC that doesn’t do frequent upgrades and provides full support to all end users. 3 plus years, I haven’t felt the desire to upgrade to anything else out there.