[MikeBmusic]

I totally understand where you are coming from! I recorded my first album (and started on the 2nd) with a Boss BR600. I bought a Mackie FX12-USB mixer. I found it great to be able to plug in a mic and guitar and keyboard and leave them plugged in, routing the stereo output of the Mackie to the two BR600 inputs.
When I started to use my computer to record, I could send a stereo track to the DAW from the Mackie's USB, and could pan each input left and right, and then set the DAW to record them as separate tracks or as a stereo track.
However, the USB conversion was only 16 bit (24 bit or better recommended for better headroom). I also found that there were no dedicated drivers for the Mackie's USB function, I had to use ASIO4ALL and latency (a delay when monitoring) was noticeable and no easy way to direct monitor.
That is what an audio interface will offer you - direct monitoring so zero latency, and better monitoring options, and higher bit rate.

As a consolation, I am still using the Mackie mixer regularly for live work, which is what a mixer is really for.