You can decide for yourself which gives the best record quality... that will be subjective. What we can do to help you is ensure you know what is in play so you can experiment without hurting any gear.

Without knowing the output specs of your electric bass and six string electric guitar, we can only say, you cannot hurt anything by plugging them directly into the MOXF A/D Input.

The MOXF has one input. It can accommodate a mono or a stereo input.

The A/D Input of the MOXF can handle signals as low as approx. -52dBu — this is what the typical dynamic microphone outputs.
Your electric string instruments will be somewhat stronger in output... by not by much. Both dynamic microphones and electric string instruments use small permanent magnets and coils of copper wire to induce electron motion... both are very weak signals and therefore need help from the A/D input’s preamp.

The MIC/LINE setting can be thought of as a Pad. It changes the range of the Gain Control. Designed to protect the Input electronics.
Weak signal — set to “Mic” — you get the most boost when you turn up the Gain. Typical setting for a dynamic mic, like the SM58, would be MIC/LINE = MIC and the GAIN Knob at maximum. That would be the maximum boost and provide enough boost to bring the mics gain up to 0 (+/-2dB)

Strong signals like from synthesizers, pro audio gear, etc, (approx. +4dBu) would be considered LINE level. These require little to no help from the MOXF’s preamp. Selecting LINE is like engaging a Pad on the input, protecting it from the more powerful devices you might connect to the inputs. When you are set to LINE use the Gain knob, as necessary, to bring the level up.

If you are using a DI Box to take the hi impedance input from your bass and guitar, the DI Box can be used to prepare the signal before going to the A/D Input. Verify the output level from the DI box and set the the Mic/Line = Line. A stronger signal will not need as much help from the MOXF preamp.

Rule: always set the MIC/LINE parameter on the MOXF to match the level of incoming signal.
Remember: little magnets = weak signal = needs preamp boosts = MIC
Synths, keyboard’s, external DI Boxes have likely to have stronger signal = LINE

Which sounds better... for you to decide.

Thank you Bad Mister for your reply. Very helpful as always.