I don't have an Apple, so I may not be the best source of information. But, I've repeatably read where AVCHD and Apple don't always get a long well. It has more to do with corporate politics than technology.
My first suggestion is to forget HDWriter if you are an Apple addict. It is made to run on PCs. Sony is the same. Their software only runs on PCs.
My second suggestion is to look in your camera manual for the Apple compliant setting for file format. I forget what it is called, but I've read that it is almost as good as AVCHD. Some may think it is better.
My third suggestion is that if you still want to use AVCHD formats, you buy Adobe Premier Elements 11. It runs on Apples. Buy the boxed set, don't download it. If you wait a month, version 12 may be out. I use it on a PC and think it works wonderfully.
If you are not using HDWriter, you only need the big files on the SD card. All the rest are for HDWriter. All you have to do is copy the files with your Apple copy utility. I've read that the latest version of iMove can do better with AVCHD, but am not sure. Final Cut Pro (for Apple addicts), in its latest versions, is also supposed to do better.