I bought a Focusrite 18i20 yesterday for this very feature after being a Presonus interface owner (Firebox, Firestudio Project) for ~15 years.
My two FSPs are basically bricks after having to upgrade my laptop, since firewire is no longer supported on modern laptops. The consensus online for whether the Firestudio Project could work in "standalone" mode was inconclusive (and discouraged by PreSonus personnel on this forum).
Loyal PreSonus customer here, but you lost one over disabling/not supporting standalone feature in your old and new interface products. Please address this guys--the Focusrite 18i20 is selling for the same price as your 1824 and $100 less than your Quantum 2626, neither of which can work in standalone mode.