From the Fireface UC product website:
The Fireface UC features 2 balanced microphone inputs with a digitally controlled input stage, individually switchable 48V phantom power, and Neutrik Combo connectors for XLR and TRS. These can also be used as additional line inputs. A pre-amplification of up to 65 dB (adjustable in 1 dB-steps over a range of 55 dB), exceptional EIN (Equivalent Input Noise) performance even at low pre amplification settings, and extremely low THD+N let these preamps surpass many reference devices. All level settings are 100% reproducible and can also be comfortably adjusted by software. Inputs 3 and 4 are flexible universal balanced inputs. They operate exactly like inputs 5 to 8 on the rear and can be adjusted to accept standard studio input levels (+4 dBu, LoGain). The input impedance can be switched from line (10 kOhm) to instrument (470 kOhm), and offers an additional analog input amplification of up to 18 dB in steps of 0.5 dB.
Digital volume changes are possible with the integrated hardware mixer - and every audio software. The value depends on the routing setup.
For the specifications please read the product website and the manual.
best regards
Knut