-= Is Avira[on demand]+Avast[on access] a bad combination..?
The problem is that avira isn't designed to be an on-demand AV but a resident on-access AV, so simply disabling the on-access scanner is unlikely to also disable/stop the loading of the low level drivers. It needs some hacking to make avira on-demand only, I doubt that you have jumped through those hoops, I don't know the full proceedure to completely disable it.
I never thought it a worthwhile exercise, when it is possible to use on-line scanners as a second opinion scan, so I never investigated it further, though some in the forums have.
RejZoR's Website - Security Ops
On-line Virus Scanners and other useful Links
Security-Ops.eu.tt