In 4/4 time that means you strum 8 times before you have to change the cord if you strum on every quarter note.
I believe you have a typo here. I believe you meant that you strum on every 8th note. If you strum on every quarter note the you would strum four times a measure. Note that I consider a strum one stroke, either down or up.
In my example I was using an 8 bar loop. Changing the chord every 2 bars. so there would be 8 total strums in the 2 4/4 measures.
For example
count in.........
4/4 Tic Tic Tic Tic
..1 2 3 4 5 6 7 8.. 1 2 3 4 5 6 7 8 (dots inserted to keep the numbers inline with the strums)
| A / / / | A / / / | D / / / | D / / / | Repeat
However the original post solved his problem by turning up the BIAB sound so they could hear it over their instruments. If someone else is reading this post practicing along to BIAB songs is easier if you use headphones, as a individual player. As a group several companies sell headphone amps that allow multiple users to plug in and play and listen all at once. These units are great for practicing at low volumes in an apartment for instance. The only set back is the drummer who is not using a digital drum set.