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The problem is that you need a harness to ensure that the stock Bose speakers continue to operate properly.
I used the GM CRV1 (replaced by the GM CRV2) for my Pioneer system but I think both of those adaptors are now discontinued. There is another adaptor and I'll try to find the details for you.
If you plan to replace the speakers then there's no need for the adaptor.
If you haven't found it there's an audio section of the forum. Some great experts on there who will answer your questions specific to your new head unit.
Take a look at post #45 for a good generic audio fitting thread: