That's an interesting choice.and it has an interesting name "Brick Wall" Sounds like it reproduces stronger echoes, not?
In theory, 7 is very similar to 3, but has less echo than it.
1 is really similar as well. They basically have some pre-echo and some post-echo, they are like an enhancement for each musical note.
2 might be the most precise one, with the least post-echo
4 has almost no pre-echo but has some post-echo
6 has no pre-echo, but has some post-echo
The idea is that musical notes look better with this so-called echo, what is basically happening, some of those enhance the texture and sounds a bit so they sound better, it hides some mistakes and things might feel more musical.
Brick walls aren't exactly the most musical types of filters, but they are usually the most precise, same for Fast Roll-Off. Those two basically keep up the sound the same until the very end, after which they roll off. Slow Roll-Off usually means that there is a gentler slope, leading to a more musical sound (to some it sounds more musical)
The differences are EXTREMELY small because iBasso implemented all of them so well, so you shouldn't lose sleep over picking a digital filter, but think about it as if brick wall and fast roll-off are the least enhanced versions, everything else enhancing the music a bit.
I might be confusing them with something else from other devices, it'd be good if we'd have a guide to what exactly each one of them does. I am talking mostly out of experience with digital filters in general, and experience with iDSD BL, which has enhancement properties.