There's a couple different areas for audio: DSP algorithms vs asset management and intelligent audio playback.
DSP is about filters and fourier transforms and HRTF and all that fun stuff.
Good DSP Resources:
Rab already mentioned this, but it's so good I have to repeat it. The Audio Programming Book by Richard Boulanger and Victor Lazzarini is probably the best place to start. Also functions as a pretty thorough introduction to C. The beginning may be a little slow for you, but it discusses some (occasionally outdated, occasionally not, but always useful and interesting) C idioms as well as introduces some sound fundamental things about sound you may not have gotten before.
musicdsp.org: An archive of algorithms, usually in C
MUSIC-DSP mailing list at Columbia
dspGuru Tutorials
Who Is Fourier?: A really interesting book written to give you real fundamental understanding of the fourier transform. Written purely with the intention of exploring how to explain complex mathematical concepts to young students. As a result, if you're a little weak on your higher level math, this will help you grok everything.
Digital Signal Processing Primer by Ken Steiglitz
Since you've done Objective-C work, check out Apple's AudioUnit Programming guide
On the other side of things, "asset management" is a little vague and mostly has to do with dealing with container formats, codecs, and streaming. Perceptual codecs is the real meat to study here. Fortunately I don't have much to offer there (seems like you need a PhD to understand most of that stuff). But there's plenty of libraries/APIs for getting the job done:
Intelligent audio playback is other fun stuff. This isn't terribly mathy like DSP is, and what you end up doing a lot of the time is dealing with voice management and music cues. There's not as much specific technical knowledge, it's more about design, and creating the tools and playback systems to support that design.
...Brian Schmidt's immortal comment "Anyone who still thinks there's a 1:1 relationship between a sound and a WAV file just doesn't get it."
Download Wwise and just start reading their docs for both the authoring tools and the API. Do the same for FMOD Designer and FMOD Studio.These give you an idea of "upper tier" tools that game sound designers use to implement content.
Another good one to check out is Fabric. Basically, Unity's audio pipeline kinda sucks, and this plugin tries to make it better. You can get an evaluation version for free.
As a musician, imagine the ideal interface you want to describe interactive game music and sound effects with, that's what these tools aim to provide. If you're familiar with what's already out there and how it supports sound designers and composers, then you can start to think of your own solutions for how to do things better.
Other resources:
Peter "pdx" Drescher wrote an awesome article about implementing the FMOD Designer API on Android with JNI.
IASIG and iXMF, the as-yet-unfinished interactive music specification standard with some interesting ideas.
Game Audio Relevance Assorted bits of game sound design and audio programming
The Game Audio Tutorial A book aimed at teaching sound designers to implement sound in UDK while teaching game sound design principles. A lot of it is about fighting UDK's audio and Kismet, but once again it's useful to see things from the non-programmer side.
http://www.procedural-audio.com/ <- Self-explanatory link
