"XLR mics" are a pure electrical representation of the source (diaphragm of the microphone pickup). Analog - No converter. USB is digital but at some sample frequency (44.1, 48, 96, 128, etc. ) with a converter. Remember both the original audio source to the mic and the ultimate destination (your ears) are analog. The only reason to convert at any point to digital is to change the source (add reverb, EQ, compression, limiting, delay, doubling, flanging, etc.) you can always do that to your analog source in Logic or Pro Tools, GB, etc. but why use a relatively cheap converter built in to the mics' USB spec rather than a high quality ADC? I would always choose XLR.