I am surprised a studio owner or studio user would post such a clearly novice question. Did you not have a clue what you were buying or how you would be using it? Have you read the manual? These are very basic things one needs to know and understand before you go any buy something like a digital mixer.

You have 2 options.

1) Use the analog and/or digital ports of the DM24 with some sort of audio interface

or

2) See if you can still get the firewire option for the oboslete DM24.