Believe it or not, a more expensive speaker doesn’t necessarily mean better sound, especially with a proprietary stock system. You have to match the ohms of the stock speaker (which can be anywhere from 1-5 ohms). That is often a challenge with stock speakers. For example, let’s say the stock speaker is 2 ohms and you replace it with a 4 ohm speaker. At the same output, the new speaker will be 1/2 as loud. Reverse it and the new speaker will draw too much current and possibly blow the amp.
Finally, you need to remove the entire door panel to access the speaker. You are under warranty so just take it to the dealer. I highly doubt the stock speaker on the McIntosh system is $35. A woofer on my Lexus Mark Levinson audio system is $470.