To be kind to Boss I would say that most of the preamp models are bit too bright sounding.
I mean it's not what I call a warm sound.
My old Line6 Pod Pro had a
lack of highs but it was more a dull sound than a warm sound. In contrast to the Line6 Pod Pro the Boss GT-8 & Boss GT-10 have to much highs which are also not warm sounding.
Use the equalizer to reduce the unnecessary highs for a warm sound without getting a dull sounding amp emulation.
In general playing rhythm guitar with high gain sounds is critical because distortion works like a compressor. You loose the dynamic of your playing. Therefore every good sound engineer will ask you to use less gain for your rhythm parts.
I will talk about two key areas of the Boss GT-8 & GT-10 multi effect processors.
Some examples: