What you are talking about krmathis is not quite what I had in mind...I know that if you set a certain bitrate target, a multi-pass encoding scheme can distribute the bitrate more for complex passages and less for simpler ones to keep a consistent bitrate. What I am talking about is having a program analyze the uncompressed stream and determine what bitrate would allow for the best quality signal for the least amount of data used?
What I am thinking is an analysis that rates how true the compressed signal is to the original combined with how high the bitrate is. For example...on a scale of 1 to 10, a lossless compression might score, say a 7, because it stays perfectly true to the original, but it requires a large filesize. A 128 kbps lossy encode might score the same 7, because though it is much adulterated from the original signal, the reduction in filesize makes up the difference. Say a 192 kbps lossy encode scores a 5, while the 256 kbps lossy encode scores the highest at a 9, making it the ideal compromise between bitrate and filesize.
That way, you would know at a glance how much compression you would need to realize a maximization of your PDAP audio space and ensuring a good quality.