LinuxMusicians

Hi,
I'm going to buy M-Audio BX8 D2 studio monitors (by the way, is there something better in the same price range?) and I need an audio interface. I already own a Focusrite Saffire PRO 40 so I don't need inputs, I just want a cheap USB audio interface with two balanced XLR/TRS 1/4" outputs and a volume knob.
Any suggestion?

I am searching for something like ARX USB-DI vc but less expensive.

Alternatively a cheap DAC with two balanced TRS 1/4" / XLR outputs, volume knob and S/PDIF input (my motherboard has SPDIF output) would suit my needs.
I want something easy to find and CHEAP. Nothing?