Imac and Apogee a must ?

You don't HAVE to go with Apogee, but their units supposedly work closer to Core Audio than others brands. I currently use an Apogee Rosetta 800 (w/a X-Firewire card), and it works great. The software driver is the easiest to use I've ever seen.

In the past I've used an M-Audio Delta 1010, and also a LynxTWO. Both sounded great, but had certain limitations. The Lynx driver, for example, could not send mono to an individual output... any mono track was forced to one side of "ganged" ports, such as 1 AND 2, which made split stereo files difficult to manage... but I digress...

Apogee is not a "must", but you're definitely safe going with them, and I'd say IME they're worth the extra money.

All the gear you listed are external synths with MIDI output/input.

MIDI is not audio. MIDI is small amounts of data (instructions) that tell the synth to playback your performance. (note lengyh, velocity, controller changes...etc) Much like a glorified electronic player piano.

So, to use the equipment you've listed... one of the things you will need is a Multi-channel MIDI interface.

Start there... do you have GarageBand... if you're completely new, you've got a lot to learn, you might want to start with what you have, you will need a multi-channel MIDI interface.

Learn to record/edit MIDI performances, monitor through your mixer.

An audio interface will give you higher quality audio than the built in I/O, but that's audio, it's not MIDI.

pancenter-

Hahah I didn't notice that you're confusing MIDI and audio...whoops! Listen to Pancenter, he knows what he's talking about.

FOR MIDI, I use four Unitor8 MIDI patchbays (they're great, but old and mostly defunct, so I don't recommend them for a new guy 😉

These patchbays are connected to my external synths. MIDI protocol instructions are passed to, and received from, these synths to my computer via the patchbay.

HOWEVER, the audio from the synths go straight to the mixer, then my speakers.

A basic audio interface converts digital and analog audio back and forth:

MAC/PC digital audio <----> Audio Interface <----> MIXER analog audio

...and has NOTHING to do with MIDI.

Some audio interfaces have MIDI ports on them, but don't let that confuse you. These units are multi-purpose units... and perhaps the best for most entry-level users.

That might be TMI, but maybe it helps.