Of course you will loose some audio quality - e.g.
SSL B6:
Dynamic Range
DAC A-weighted 117 dB
ADC A-weighted 117 dB
Apogee Symphony MKI
Dynamic Range
DAC A-weighted 129 dB
ADC A-weighted 120 dB
The apogee converters for example have some very musical sparkle in the top end, which the B6 converters cannot provide.
The consequence for you depends on your personal expectations and your workflow. If you come from a high end setup and switch to the B6 you will either loose some audio conversion quality (when using the internal converts) or flexibility (you cannot track 16 channels at a time with B6 when using external converters e.g. tracking via INSERT OUT 1…4, Bus B, Main Out since there are no direct outs for all the 12 input channels available).
If you come from a mid-range setup, the B6 is a step up - audio quality wise.