IPP AAC Encoder supports MPEG-2 AAC standard and any AAC player should be able to play it. MPEG4 AAC has some additional fetaures which are not used by IPPEncoder. If you'd like just to have an "MPEG4" word in your stream viewer (or whatever you use to watch stream info) let me know and I'll tell you the line in codeto change. As a result only one bit will be changed in AAC header but the data itself will be the same.
Concerning problems with playback, I don't see any problems with your code. Besides I've just encoded a stream myself and it is played by QT without problems. I use 7.6.6(1671) version of QuickTime.
If you still have problems you can sendyour stream to investigate the issue.
I recently came across this problem as well. I was using Quicktime version 7.6.4 and after seeing your post upgraded to the latest Quicktime 7.6.8 and with the new version it works. So Apple must have added some functionality between 7.6.4 and 7.6.6 to play certain types of aac streams.