Theres likely better people here to help you than myself, but Ill step in until someone has better info or another perspective.
All processors are or can be used as preamps, but not all preamps can be used as processors.
Although it can be construed that a preamp does process the signal in the broadest of terms, it seldom changes the signal apart from adjusting the signals amplitude or inverting it's polarity. Processors do more.
The conotation of the word processor means it actually processes or changes, one signal into another. Usually by decoding the incoming info and outputing it into some other format. often these processors are multi ch oriented... not just 2ch.
Im unfamiliar with what Mac offers by way of multi ch. They change often, and lay outside my $$$ reach much of the time.
Ive owned a few receivers. I always felt the (previously) tradeoff of sonics vs. versatility were acceptable to me. Currently they offer far better audio used strickly as 2ch preamps
. Pretty much across the board. Of course there are always exceptions, and not all are alike. Though the 2ch audio representation they many afford one now is as best its been, and can be said to be over achievers.
A dedicated processor IMO does only that
processes the audio and video input signals for output to some other dedicated device (s) ie., amps & displays. Some are upgradeable via firmware for newer audio formats (CODECs) so they possess more utility and longevity.
But thats all they do, decode, pass thru, and output. A source unit or more are needed, eg., blue ray disc player, cable or satellite box, DVR, DVD, CD, DAT, tape, etc.
To cut costs and get up and running quickly, many choose to go with the trusty receiver initially. Eventually, it will become merely a dedicated processor as external amps are added thereafter, and its sole duties are then preparing and decoding those input signals as best it can.
HDMI 1.3a outfitted receivers or processors decode the newer high res audio formats thru that one cable interface. Yayy
less trouble and way less $$$. Nearly true 'plug & play'.
The thing is this, IF the processor has HDMI 1.3a, AND multi ch RCA inputs, you should be fine with current norms.
Probably for another four OR FIVE years or so anyhow. MAYBE MORE.
Past that if the maker of the multi ch processor will not or does not allow for future upgradability, one must then buy a 'THEN' current source device which does do the decoding itself.
The only upcoming change I can figure out for either receivers or processors, is networking and high res audio handling of computer based or hard disc drive files
some do that now like the new Marantz sister co of Dennon.
Many receiver makers offer the preamp/processor portion of their receivers as dedicated units
no amp, sometimes no tuner either. Often this separates approach is seen as advantageous. Mo betta
. Than all in one receivers. Onkyo, Integra, Marantz, Anthem, and a ton of others make them in all sorts of price levels and ability levels. Some do video better than they do audio, or as well. Some emphasize or dote on the audio and allow for so so video and so forth.
Ya just gotta look around some and do a bit of leg/web work to see whats what lately.
