Bschorr, I also would like to hear a sound clip of these.
Here you go, Fatboi. Corsa's site has the sounds for all their catback kits (at least the ones I've looked at). There are several different clips of the exhaust under multiple conditions- idle, rev, launch, drive-by, and dyno.
The problem is, the exhaust kit for the Seville won't work on an Eldo because the plumbing is different. You can modify it to work, but it's still going to be difficult.
As Gizmo and others will say, you can get a set of dB mufflers to replace the stock ones. They sound nice (there are a few sound clips of other cars with them on the site as well).
As far as the exhaust is concerned, GM did a good job. There are a couple things, in my opinion. The plumbing BEFORE the cat is one of the areas. It flattens out a bit to fit over the oil pan. I haven't looked at it in depth, but there's probably a way you could reroute the plumbing. Not a big change and won't make that noticeable a difference I'm thinking.
Also, I'm unsure on this one, but the Y joint seems to be a little sudden. You might be able to improve it by putting a more gradual split in? I'm not an expert by any means, though, so I'd ask for some other opinions... Again, it won't provide that noticeable a change.
So basically, if you want a good sound and slightly better performance, replace the mufflers with the aforementioned Corsa or Borla.