I think you got your MacBook Pros confused.
The MacBook Pros use a mobile i7, the iMac uses a desktop i7, the desktop i7 is faster.
The classic MBP does not have an HDMI interface, the MacBook Pro with Retina Display does have HDMI.
The MacBook Pro with Retina Display does not have Firewire nor does it have Audio In. The classic MBP has those two.
Firewire is looked upon as dying port by Apple, it will disappear once the classic MBPs get discontinued in one or three years.
Why the Mac mini has those ports though is another matter and for audio recording there are much better external DACs out there than the one Apple offers inside their Macs, even at reasonable prices.
And only the base iMac has worse GPU than the MBPs, the higher iMac versions have the same and better GPUs.