Converge/mix 2 audio streams?

[Guy Abandon.]

Hi all.

I am hoping to describe the process I am trying to achieve, so that
suggestions of how to achieve it will give me the necessary leads. Man, Help
and Docs assume a prior specific knowledge; if only on what tools to read
about.

My objective is to:-

1>  convert and stream a collection of .mp3s sequentially into a single .wav
and hopefully, normalise to a lower volume level in the process.

2>  having done the first step into a pair of long .wav's; to them stream
both in parallel or mix them into a third single .wav...   maybe even a long
single mp3 but that can be done as an additional later step if necessary.

The key bits are - to sequence a collection into a single entity, normalise
such an entity, then mix a pair of such entities into a third single blend.

For those really interested, I have to put backing music to a lot of
verbalised text.

Any thoughts please?

GA!