As is obvious from my earlier message in this thread, I wasn't even aware that the Beginner's Book came in an audio version. Thanks to all for pointing this out.
I agree that it would be great if Mauricio and Amy create some more advanced audio lessons. I'm not so interested in an audio version of the Advanced Book, but rather lessons primarily in Spanish to help me improve my ability to speak and understand spoken Spanish. However, I'd also like to recommend some lessons that already exist: *Learning Spanish Like Crazy* at *__http://www.learningspanishlikecrazy.com/__*. Though Learning Spanish Like Crazy is intended as a beginner's course (and I came to it as pretty much a beginner), it's really a good follow-up to Rocket Spanish. The speakers on LSLC speak carefully but much faster than Amy and Mauricio do; you hear the opening conversations of each lesson at something like normal conversational speed. The lessons also cover a lot more than Rocket Spanish. For example, by the time I was done with LSLC, I had learned not just the present tense but also the preterite, the imperfect, and the perfect, as well as reflexive verbs and lots of vocabulary not encountered on Rocket Spanish. In fact, I found that after Level 1 of Learning Spanish Like Crazy, I had covered more than after completing all three levels of Pimsleur (another program for learning Spanish, which I was able to get from my public library).
Like Rocket Spanish, Learning Spanish Like Crazy is available both to download and, for a lot more money, on CD. The download version of LSLC is similar in cost to Rocket Spanish. Like Rocket Spanish, LSLC has a useful web forum. Also like Rocket Spanish (and unlike Pimsleur), LSLC has printed material that enables you to see what is being said on each lesson. It doesn't offer the wonderful array of other materials that Rocket Spanish does, but it does throw in levels 3 and 4 of the FSI (Foreign Service Institute) Spanish course.
I think that Rocket Spanish can't be beat as a beginner's course, but I would highly recommend Learning Spanish Like Crazy as a follow-up. (I might add that LSLC will soon be coming out with a more advanced course. I don't have much information about that, except that among the things it will cover is the subjunctive.)