There is no such thing as "blu-ray quality audio", nor is "HD audio" a codec. Blu-Ray supports a variety of codecs, including AC3 (AKA Dolby Digital). It's part of the spec, so AC3 is by definition "blu-ray quality".
What I think you probably mean is that the quality is not as high as the lossless codecs. Bluray supports three of those. LPCM, which is uncompressed, and Dolby TrueHD and DTS-HD for compressed. Either of those three will provide identical quality, since they're all lossless.
To most consumers, the difference in quality between even AC3 and lossless is indistinguishable. For those with both a high-end home theatre system and a discerning ear, higher-end blu-ray rips often include lossless audio, although these rips are often not much smaller than the original blu-ray themselves. You'll sometimes find the audio transcoded to FLAC, another lossless codec which is more efficient than Dolby TrueHD or DTS-HD.
The most typical scenario you find is the rip will simply include the regular DTS or DD+ stream. I'm not sure that anybody can actually tell the difference between DTS and DTS-HD in practice. You'll get a much bigger difference in audio quality from the quality of your AV decoder's DACs than you will from the DTS/DTS-HD difference.--
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