Is there an interface that I can add that has multiple inputs for guitar, mic, etc.?

Hello,
 
I recently purchased the Roland Quad Capture USB audio interface and it works great!  I moved away from the Creative X-fi Titanium internal card.  I noticed the difference right away in the quality.  I am using Platinum as the DAW and am wondering if anyone knows if there is an interface that I can add that has multiple inputs for guitar, mic, etc.?  What I want to accomplish is being able to record the guitar on the first track and while playing the guitar, record the vocals into the mic plugged into the second track.  I started off with a Fostex 280 in 1990 and I used to be able to do this; play guitar and sing at the same time on separate tracks.  This helped me keep in time while playing the rhythm.  My demos are simple, mostly guitar and vocals but I am hoping that if there is an interface with multiple inputs, I can expand my demos.
 
Thanks!

^^^^ agreed. From what you have described, you may already have what you need. Take a look at input routings to SONAR.

As above, most interfaces will work, providing they have a preamp and a DI for guitar (the "preamp" is short for preamplifier, which brings a mic signal up to line level while a DI does the same for a guitar signal).
 
You can "stack" Roland units, as above, for more inputs.  You can get an interface w/ more inputs (2/4/8/16 are the usual numbers, going back to tape track standards).  Or you can add more inputs via digital ins and outs.  I don't know if yours has a stereo  SPDIF or AES connection (or ADAT, which is 8 digital in/outs over a single cable) but I added a TASCAM uh-7000 stereo interface via Spdif to my TC Konnekt interface because it is a higher quality convertor and has really great preamps.  And it is (relatively) cheap for the quality.
 
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