Have you tried using the respective channels (clean, crunch, insane etc)?
I use a line6 pod2. The only line6 tones I use from it are the clean and the insane.

line6 flextone III !!!!!!

line 6 insane all the way

use clean setting or something like the fender bassman or the double reverb for a nice clean sound. bugs me though. it sounds too clean, so i throw in a little drive.

but the flextone 3 does :)

yeah I have a spider III amp

Joe... Your sound is in your ears. Just because someone else has the same amp doesn't mean their settings will work for you. Maybe if they're playing the same guitar, with the same strings and the same hands... It still amazes me how many people think their tone is in their guitar or their amp, but it isn't.

What you need to do is learn your gear. Using someone elses settings doesn't teach you anything. Messing with it yourself does! You get to hear for yourself what each knob, dial, switch, pot, does. You get to adjust them to YOUR taste and that's what it's all about in my book. There are WAY too many people out there trying to sound like someone else. Thinking this amp or that guitar will make a difference. It all comes down to practice. Not just with your guitar, but with all your other gear as well.

Just my 2 cents.

The AC/DC sound has more to it than just the amp. If you had another line6 product I'd tell you to look at the JCM800 model. I don't remember what exactly the models in the spider are, but find one that distorts quite a bit and in a crunchy way (the model right before the insane should do that) and mess with the EQ, gain (cranking it all the way up isn't always the right answer), guitar volume and pickup selection. You won't nail it but after some experimentation you should be able to find a setting that fits the general idea.

I'm not familiar enough with U2's sound.