Unmodified Blu-ray disc images are the BDMV folders I mentioned. Any BDMV will be unmodified almost all the time though I've very occasionally run into modified ones originating from the Chinese piracy scene that had custom subs added.
A "good" remux is actually the highest quality movie release available, usually, if you don't care about file size. A good remux will combine all the best parts of every possible release into one super-file. For one movie, you could have the best video quality be on a French UHD Blu-ray, the best audio quality from a different source, subtitles aggregated from various international releases and streaming platforms (and filtered/deduped for quality), chapter titles taken from an old DVD, and all available commentary tracks collected. Rarely you might even see a hybrid release where multiple streams are spliced together to fix some problem or another in one of them. You can look for releases by the CINEPHILES p2p group for gold standard examples, they get distributed fairly widely so you can probably find some.
To answer what you asked about extra audio tracks specifically (outside of full disc images)--usually non-English dubs are considered bloat and aren't distributed. Commentary tracks are kept. Audio description is a mixed bag, good groups will keep it.
