You couldn't take advantage of both because the StudioLive doesn't have multichannel digital outs or ins.
They are completely different products. Think of the StudioLive as a Live Digital mixer that also happens to have great audio interface capabilities. The Ensemble is a great audio interface that also happens to do mixing.
As far as the sound of the conversion goes, the Ensemble does sound good. Apogee has a sound that lends it self to being more analog in tone. Presonus' philosophy is more that they are trying to be transparent. This really isn't perfectly apparent when you just listen to stereo in and stereo out, it is really when you start to spread this over many, many inputs and outputs.
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