I do not understand your concern about AGPL. You seam to believe that connecting a proprietary system to an AGPL service is prohibited. It is not. AGPL only adds on top of usual GPL that source code must be available to remote users even though they do not exactly receive the software. If you do not plan to modify the AGPL software, or if you do not plan to hide those modifications from its users, then I can't see what's the issue.