What software it is?
I've am degree in computer science, decade and half ago I used to run analog circuits simulations thru pspice, math cad etc, many times I simulated circuits with tube amplifiers, and all this was done on my powerful 486 pc with obscene 128 mb of ram, those simulations recreated with high precision every wave, so I'm curious why some audio simulations today requires that much cpu time, maybe the software was so inefficient coded or the simulations it's focused on animations than the true comments of the audio signal.
He must be running Cubase, that is the worst and laziest coded DAW software I've ever used (despite a great feature-set). Add in some bad plugins and him over-processing things with large chains over many channels and an i5 could easily get bogged down.
I have the 2.3 i7 mini in a studio environment with a 256gb SSD set up in fusion mode, running Reason 7 and it absolutley flies. I've also never heard the fan turn on since the day I bought it btw (about 1 month ago, yes I gave up).
With an SSD the 2012 model is still a very capable machine. It should be fine for anyone wanting to use it for work/internet and anything that is not 3D modelling/heavy video work or gaming. If you are serious about gaming though you still need a PC, just for the sheer volume of titles that are PC only.
That said, I'd love nothing better than a concerted effort by Apple to create a Gaming Mac and a push for AAA devs to start releasing native Mac versions of new games. I'd love to be PC/Windows free at home.