[Junk_Collector]

The core of EE is Fourier analysis and BCI is no exception but you should be strong there because you've studied applied math. Most of your target books are good after your HN update, but one thing you are missing that will probably make a big difference are some books on measurement science. You'll want to get some focused both on EE and biomed/biology because they will focus on different things and both are relevant to your interests. Eventually you'll also want to touch on some non-linear and statistical control which play into the implementation of the more modern cutting edge BCIs. DSP overlaps a lot with this but still has some uniqueness you'll need to learn to put things into practice.

Just an FYI, a lot of BCI companies are running stuff like repurposed audio analyzers ala the U8903B for lab work and bench testing their designs. Parallelism is the name of the game, and analog performance requirements aren't super strict so you won't be designing custom ICs any time soon unless you want to work on the probe interfaces themselves (which are more MEMS than circuit design but need a little of both).

Something like Medical Instrumentation: Application and Design by Webster is a great place for a beginner who wants to toy with human interfacing circuits. Back it up with something like The Art of Electronics and that will get you to professional lab tech territory.