Some AVRs do have a "Direct" or "Pure" mode bypass that just redirects the analog input straight to the pre-outs and/or amplifiers other than basic volume control. You typically lose your delays, bass management, etc on those models in that mode.
I personally don't buy into the notion DAC differences are actually audible at this stage of development. The differences are too small and so I wouldn't bother, but whatever floats people's boats I guess.
Yes - many (most?) have a pure/direct mode - but that bypasses all the processing functions including things like crossovers.
Some AVR's of 10 to 15 years ago, had jitter issues, especially with HDMI input streams (not so much with SPDIF/TOSLINK) - which might (!) have been audible.
Current generation AVR's don't have this issue (in fact on some of the current ones, the SPDIF/TOSLINK performance is lower than what is achieved on HDMI... time marches on!).
Most current mid market and up AVR's have DAC's where the sound quality should be indistinguishable from any other quality DAC... flaws such as they may be (SINAD, THD, Noise, Jitter) are all below the threshold of audibility even on mass market chipsets.
Some parts of the audio chain, are really solved problems nowadays, and short of an engineer really messing up, there is no excuse for an AVR to have below par performance in DAC terms (par being measured based on Thresholds of audibility... - yes most AVR's do not get close to the SINAD possible with SOTA stand alone DAC's.... )