I’m not entirely sure it’s seamless. The color timing of the live action shots is much less saturated in the unaltered versions. Also, they only use the original mono audio.
I thought they match color wise very well, or at least to the degree they did in the SD masters (optically composited special effects are always going to look a bit different from the live action stuff).
You can switch from the mono to the surround track with your remote if you want. (The reason they don’t show this option in the menu is because the stereo pans are based on the new shots of the Enterprise rather than the old, so it can be disconcerting. The mono sounds good.)