I have a C1 on my second machine(the one that does this stuff:-) which I do use occasionally for bits and pieces, and a UR824 on my studio machine, the 824 is the same as the 28 quality wise just with extra inputs I think. The advantage you would have with the UR28 is 1) The pre's are better to my ears, not a lot in it but,,,,,also the firmware includes the Channel strip which is very nice and uses no CPU power plus the guitar amps,,,,ditto re the cpu power. Plus the ability to control the Control Room routing and levels from within Cubase or with the dsp software. The C1 is OK but the UR is somehow more "Pro". Hope this helps, only my opinion though:-)
Entertainer | Musician | Producercricket@iafrica.com
Computer i7 3 Ghz CPU, Intel Mobo, 12Gig RAM System Drive115 Gig SSD + 4 x 1TB recording and sample drives.
Software: Win7 64Bit Cubase 7
Interface: Steinberg UR824 with Focusrite Octopre, Steinberg CI1 on spare machine
M-Audio Keystation Pro88 Controller