The Mjolnir like the Lyr is just a head amp. No DAC inside, so no USB connection.
You can use a mini stereo to RCA jack to connect the computer to the Mjolnir. The Mjolnir supports either RCA or balanced analog inputs (not both at the same time). You just flick the switch depending on which type of input you use.
Or you can use the matching Gungnir DAC which does have a USB input and has balanced connections to match the Mjolnir.
I use the Mjolnir on my bedroom setup with a Bel Canto DAC3.5VB II/VBS combo - connected to my MBPretina using a Wavelink HS.
You can use a mini stereo to RCA jack to connect the computer to the Mjolnir. The Mjolnir supports either RCA or balanced analog inputs (not both at the same time). You just flick the switch depending on which type of input you use.
Or you can use the matching Gungnir DAC which does have a USB input and has balanced connections to match the Mjolnir.
I use the Mjolnir on my bedroom setup with a Bel Canto DAC3.5VB II/VBS combo - connected to my MBPretina using a Wavelink HS.