How to input such system
into maple so that it would solve it?
BTW we some part of system will be given to us, which we do not know certainly - may be some $A_i$'s may be some $B_i$'s as constants. We do not know how much constants we will get. And we would need from given constants get a solution for other $a$'s and $b$'s. In real life we will be provided with $s$ as a constant but I hoped for general solution=)
Apparently you want your solution be parametrized in $k,s$. I don't think Maple can do that. What you need to do is to solve this linear system for some particular $k, s$ and hopefully you can discern a pattern.
You can solve linear systems using the linear algebra package: >with(LinearAlgebra); or >with(linalg); the last one is deprecated.