Don't be sorry: there is some tool designed to do something, and other for other things. You don't expect that your everyday car will fly. It would be the same thing if XO was working in the browser only. We made that choice (to have a server part) because we knew we'll push for features requiring to run 24/7.
You can boot a VM on PXE by selecting the right boot order (enabling "Network" in boot order in XO for example)
Then you need to setup a PXE server, you can fine various guides by googling "PXE server setup", eg this one)
@schories It should be noted here that the emulated BIOS in XCPNG7.6 seemingly doesn't care about the bootflags. If the first one (per device id) isn't bootable it will fail, even if xvdb is bootable! So if you e.g. have swap on xvda, move it to another device id at the end (and temporarily disable it in fstab or so)