For naturalness you need a very dynamic and unforgiving speaker. Preferably a pro studio monitor, active or passive. Great suggestions would be ATC, Westlake, Quested, PSI, Unity the Boulder, Barefoot, dual centric Tannoy and many more. Westlake is a "new" favourite of mine.
Note - with these your bad recordings will sound bad and the good will sound good sometimes fantastic. They will not all sound mediocre as with most HIFI home speakers. Your Harbeth should be ok although being a home speaker. I found it a bit uninspiring. Harbeth also have studio versions. Don't know if they are different.
If you with natural sound means concert sound, then visit a live venue. I don't want that sound in my home because it's very seldom enjoyable. You don't go to a concet for the sound. Maybe Roger Waters...
Not sure about the open baffle suggestions. Can't think of a speaker technology that interacts more with the room. But would like to try in the future.
Also, as someone already pointed out, try to find the good recordings and skip the bad. Discover new artists that really try to also present a fine sound. There are lots of them. Also the same artist may hav a big spread between good and bad recordings. Sometimes on the same cd. Listening to John Fogerty when writing this and he is a good example. Tidal is great for this.
Just my ideas and Good luck!