I'm using the Charis SIL font for the EPUB reading mode or with the EPUB reading mode

[Zoli]

Which one of these two sound natural?
1. I'm using the Charis SIL font for the EPUB reading mode.
2. I'm using the Charis SIL font with the EPUB reading mode.

Context:
The EPUB reading mode is a functionality inside a software which wasn't designed for reading EPUB files but it supports the feature through something called "EPUB reading mode."
What I'm trying to express is the type of font I'm using in this mode.

 

[Barque]

Your sentence 2 sounds better than sentence 1.

I'd put it differently.
I use the Charis Sil font when I'm on EPUB reading mode.

 

[Skrej]

Either of the original versions works fine for me. I might choose #1 over #2 if I was discussing switching between reading modes.

I'm using the Charis SIL font for the EPUB reading mode and Payprus TTF for XYZ mode.