Thanks for sharing your setup. I'm curious about the frequency response coming off the turntable. More than just amplifying the very low output and flattening the RIAA pre-emphasis, a true phono preamp also loads the moving magnet (MM) cartridge with the official high resistance of 47,000 Ohms and capacitance of ballpark 100 picoFarads. (Pro gear often allows these to be adjusted to account for cartridge and cable variations.) The very high impedance is why turntable cables must be short and carefully arranged.
Feeding a high impedance MM phono cartridge into a low impedance microphone input on-paper doesn't present an appropriate load. For instance, a typical pro mic load is 600 Ohms. This low impedance allows long-ish microphone cables, especially when the mic-cable-input is a balanced (3-wire) circuit.
Of course, standards are on paper, which the real world often ignores. And, the specs arose in vacuum tube days, which were more sensitive to variations than modern circuits. So, in your setup, how is the phono cartridge as source being handled? Is the mic input switchable to provide a "phono" cartridge load? Do you detect any audio anomalies that the software doesn't fix?