In answer to the first part of the question (how to get more theoretical CS knowledge), I studied an extremely theoretical degree and the materials are online to dig through - if I were to self-teach now, I'd start at the final year's course list (http://www.cl.cam.ac.uk/teaching/1314/part3.html) and work backwards to chart a path to the modules that sounded most interesting.
In terms of "taking knowledge to the next level", though, it could mean anything from you wish you knew what red-black trees and big-O notation were, to you'd love to be able to design your own programming language and write a compiler, to you wish you could administer a Linux box. I would actually suggest the best approach here is to find someone with the job you want and talk with them 1:1 to figure out where your knowledge could be most improved.
Also, for Coursera, etc, there are local study groups at places like Hacker Dojo you could join to get some of the benefits of college without the expense.
In terms of "taking knowledge to the next level", though, it could mean anything from you wish you knew what red-black trees and big-O notation were, to you'd love to be able to design your own programming language and write a compiler, to you wish you could administer a Linux box. I would actually suggest the best approach here is to find someone with the job you want and talk with them 1:1 to figure out where your knowledge could be most improved.
Also, for Coursera, etc, there are local study groups at places like Hacker Dojo you could join to get some of the benefits of college without the expense.