With Bose the system ohms is not the issue. The signal from the amp is not normal. It is not equalized or have a balanced frequency response. The final frequency response balancing occurs in the electronics on the speaker unit. the final electrical output from the electronics on the speaker is tuned for the frequency response of that particular speaker and car model. If you try replacing the speaker unit it will sound terrible. I believe if you want to upgrade you must replace the entire system.