Audio interfaces - are they a real alternative?

[gorillaonabike]

So I've shot a couple of shorts now and one element I have noticed is the portability of a Tascam does not confer any real advantage. I have consistently shot in controlled areas, scouted well in advance for sound and portability has never been an issue.

Therefore, I was wondering if an audio interface linked to a Mac (MacBook Pro with souped up RAM) would confer any pre-amp advantage over, say a Tascam DR100?

For example, I have a Mac with Avid and FCP 7.something (the final version before 'X') and I was wondering if I could record using an audio interface with phantom into the Mac. In addition, I am on a budget so would wonder at what point I would be able to buy a used audio interface linked into the Mac at a lower cost than simply buying a DR-100.

As an idea of mic, I have a Sony ECM 674 and will also probably buy some lavs and maybe even a second mic.

The reason for asking this question is I had all my sound gear walk off and after an analysis of my financial situation, I am looking to replace at lowest price. This either means going back to a DR100 with its relatively noisy pre-amps or finding a suitable alternative. And naturally a bit of lo / hi-cut help is always handy.

And please note I am aware of the personnel issues around the kind of setup I am using but might be able to get around this.

Does anyone have any thoughts around audio interfaces and if so, what they would suggest which has better pre-amps than a DR100 which will work with my software setup?