Yes, if you are not confortable with installing it, you can use a portable version.
https://github.com/alexkay/spek/releases/download/v0.8.5/spek-0.8.5-beta.zip
But you will still need to click in the executable file. You can also check audio quality in video files too. Just throw in the software window.

 https://savemp3.net/3qivu/  cut's the song to 128kbps.
Tested with this one: https://www.youtube.com/watch?v=R9kK3BYlEoM
This is from an official channel, and is 192kbps+, in spek it's in the 19,5khz.

To Download i use a paid 'any video downloader', but i'm sure there will be many ways to download a audio or video with the best audio quality on youtube.

I used to use the kdramaost site. It also had Cdrama ost but it haven't updated in a while. 

What you can try if you know that these OST are officialy are released and if are possibly  on deezer/spotify you can try this site:  https://free-mp3-download.net/

It has good 320 kbps mp3 quality. Just keep in mind you might need to look for the song/albums sometimes on Chinese if they are not available with their English name and also some signs like: .,:' might not work so try to use without them.