Rick, I can't help you much, I guess. If Firefox 3.6 and Safari 4.1.3 are too old for Soundcloud you're probably out of luck with 10.4. The G3 version of TenFourFox might run in Rosetta mode on your Mac, but the browser isn't supported on Intel Macs. Plus, for Soundcloud you likely need the Flash plugin which doesn't run in TenFourFox at all.
If you want to publish on Soundcloud and your business depends on it, you'll either have to invest in a new Mac and more recent software, or if money is tight at least partition your HD (or buy an external HD) and make your Mac dual bootable with Mac OS X 10.6. All Intel Macs can run 10.6 and this OS still supports up-to-date browsers. You could then keep on producing on 10.4, and publish on 10.6. Good luck!