I don't have a lot of knowledge of music theory and I am trying to learn all by myself online. I am trying to play and sing the song Drive by Incubus on my guitar. The original song seems to be in the key of G. The chords for verse and chorus of the song in this key are: [ Em - Em9 | Cmaj7 - Em/A (slash chord) ]. In the pre-chorus, the chords are: [ Cmaj7 | A ].
This key is too high for my voice and I want to lower it by two keys to the key of E. I am trying to use the following chart to find the chords in the key of E.
If we can simply transform the chords using this chord chart, I think the chords in the key of E should be, for the verse and the chorus: [ C#m - C#m9 | Amaj7 - ? ] (I am not sure how to transform the slash chord!). In the pre-chorus, I think the chords should be: [ Amaj7 | F#7 ].
Is this the correct way to change keys for a song? What am I doing wrong? What should the correct chords be for this song, if I want to go down two keys?