Your arms do grow from compounds, but even if you did splits, they grow very slowly. I would recommend adding an extra 3-4 sets on one day of the week just for biceps if you care about them a lot.
Check around for the weight belt - sometimes gyms have one available or lying around for anyone who wants to use it. I recommend getting one if not (or making one!) Doing 20 easy dips is no substitute for 5 where you're struggling because of added weight.
its all good ordered a belt now, i hate doing extensions and not the biggest fan of pushdowns, skull crushers hurt my elbows lol so i was thinking of doing 3 sets of dips and 2 sets of narrow grip so 5 sets in total instead of 6, this sound okay?
also i my arms do not grow from compounds at all done the 5x5 program before and my tris or bis never grew
Throwing in a couple sets of arm work at the end is very reasonable. I'm all for focusing on compound movements, but if your arms genuinely can use the extra work then go for it.
As far as high rep dips go, you won't be generating the stimulus you want unless they are heavy enough. At a certain point you are going to have to add weight. Either buy a belt, or go the cheap route and just stick a dumbbell between your legs. It's weird to get used to, but very doable. I've done it with a 125lb dumbbell before, do it's quite possible even with pretty significant additions over your bodyweight.
The only time it's bad to feel the burn is when you're peeing...