A lot of people are no doubt using straight cpap just fine and getting great treatment. Just because a lot of us on the message boards choose to use autopaps, it doesn't mean you have to worry that you're not going to get "as good treatment" from a straight cpap machine.
LittleBaddow made a good point in favor of using autopap - being...if the pressure you need changes in the future (or wasn't found correctly during the sleep study titration) the autopap can find what you need, night after night, month after month.
Autopap can be set to operate as a straight cpap, if that's what your doctor and you prefer. Two types of machine in one, for not really much more money. A lot of flexibility, as LittleBaddow said. Convincing a doctor and an insurance company and a DME of that can be another matter.
But as far as getting effective treatment, Newsgrouper, a straight cpap can give you that, too. After you try it for awhile, if you don't feel that you're getting good results, perhaps you can get your doctor to let you have a trial on an auto with C-Flex to see if an autopap makes any difference.
If you can get the order switched to the Respironics Auto with C-flex, I'd do that. But if you can't, I wouldn't worry.