Easy2Boot works by modifying the \AutoUnattend.xml file on the USB Flash drive just before it boots from the Windows Install ISO.
When Windows WinPE starts to boot, in runs wpeinit - this sees the \AutoUnattend.xml on a removable drive, interprets it and then runs the LOADISO.cmd file which is on the E2B USB stick.
You should see a blue console window appear before Setup displays any user GUI windows?
The LOADISO.cmd file contains code to load the ISO file as a virtual drive - when Setup runs, it will see the Virtual DVD and not complain about 'needing CD/DVD drive drivers'
It sounds like your ISOs are modified so that they don't run wpeinit.
I suggest you download and test with a standard MS vanilla Win7 Install ISO - if that works then your modified ISO is the problem.
You can either modify your 'special' ISOs or manually run LOADISO as soon as Setup starts. See Installing Win7 under a VM for details of how to manually run LOADISO.