Well, Dave, you may have played more mouthpieces---I stopped trying at about thirty when I found one that worked for me and for my horn. No offense taken.
Can I play whisper quiet? Yes----but, what's an 'open embochure'?
I've bought horns that didn't work for me. That's why I'm curious as to why they didn't work. Dave, Trevor---et al....take a look at the article at this site:
www.smithwatkins.com
then pick 'technical articles'. The first article that comes up should be a discussion on the resonance of the bell. I found this by accident today, but it pretty much says it all for me. Read the article and see what you think.
As for making the leadpipe bigger---nope, I don't think it will work if the leadpipe is not matched up to the bell. Besides, you can only make a leadpipe only so big! :)
Bill