If you're attempting to improve audio quality by adding a ADC/DAC then you may be
disappointed, since most budget models are unlikely to provide higher quality than those
already found in typical modern interfaces.
Think about it - audio interfaces
sell in far greater quantities than standalone converter boxes, so their prices tend to be
a lot keener.
I respect SM Pro Audio (I have one of their M-Patch 2 monitor
controllers in my studio) but for them to put a ADC and DAC into a 1/2 rack case, along
with two mic preamps, and then sell it for £200+VAT means that while I'm sure it will
sound good, it's unlikely to sound any better than a £200 interface with similar
If you have a £200 interface and want to achieve better audio
quality by spending an additional £200, a safer bet is probably to sell your existing
interface and buy a new one costing £300+