You need to fade down both ends of each audio clip, to get rid of the pop.
If you want to do a crossfade, you can use Womble's transistions (I can't give you any info on that).
Or you can do it manually, like I do, and put the first clip on the speech track, and the next on the audio track, the third on the speech track, and so on. Then you overlap the ends of the clips and fade each end down.
Regular Womble will only save 2-channel audio if you blend AC3 manually (and maybe if you blend it with transitions). Or if you try to mix 5.1 & 2.0. Or if you mix bitrates.
Womble-DVD doesn't have that restriction. It saves 5.1 ac3 if you tell it to.
It seems to be true 5.1. The audio goes to the correct channels. And it does a good job of converting 2.0 clips to 5.1.
I only ran a couple of tests, but it doesn't seem to do any phoney mixing - seems to isolate a true center channel and true rear channels and true L&R (and true sub, but that's easy).
(Some freeware makes true 5.1, but some others do lazy mixing like some of the earliest pre-dolby electronics used to do - mixing just effs up your sound environment).
(And some freeware do a better job of faking, by using delays & analysis & stuff - ambisonics & ambiphonics are examples of the more advanced fake-5.1. You sometimes want to use those if your source is non-dolby stereo. But I'm digressing here).