Second that you are probably in need of a controller that works with your existing interface but adds faders, solos, mutes, pan, etc. albee1952 mentioned Avid solutions, but there are a lot of 3rd party controllers you could use as well. They mostly work with the aging HUI protocol, but still give you a lot of functionality.
Mackie MCU Pro's can be had used at reasonable prices, but the new
Presonus Faderport 8 looks promising.
Check 'em out!