Causes of long term listening fatigue?

I like to listen to music continuously for hours mostly at low volume levels. For me therefore, it is important to have a setup that will not cause any listening fatigue (lf).

Now I am looking for a new speaker setup and I wonder whether people could comment on the following aspects:
1. is 5-ch more susceptible to lf than 2-ch?
2. are there quick tests so that one can determine whether a given speaker will tend to give lf? I ask this because in a shop it will be difficult to assess this due to lack of time and differences in acoustic environment.
3. Which speakers do you know in the price class $3k that do have lf problems and which ones can be recommended in this respect? (difficult question, I know).

Thanks for input.
Regards,