There are some 5 1/4" speakers that will fit the Wing, with some cutting. I did not like the sound of the Kenwood, Sony, and Alpines that I tried. They were simply a poor match for our small cabinets. When I installed the Polk db521, I had to REALLY chop up the cabinets, and they sounded awesome. But...... when done, I could not install the instrument cluster cover. I had to undo that one and replace the speaker cabinets. Lesson learned.
The problem with Polks is that they use long throw cones, which require wider, oversized baskets. It also strengthens the frame and improves sound. Little details like that are why Polk speakers have such a great reputation. The basket is almost bigger than the diameter of the cabinets. You can't use just the cutout hole size a final determining factor. There is more involved to it.
I settled on the 501 years ago because they sounded much better than any of the 5 1/4" speakers I tried. I have recommended them for years, and a high percentage of my customers have loved them. Make no mistake. The size is a compromise. But it is the best alternative I have found.
A previous post was correct. Keep your expectations in perspective. We have small speakers in the 01-05 bikes. That limits bass, and volume to some extent. The radios with the bad amps in them sound muddy and have no punch at all. The high quality amp I use improves sound quite a bit, and gives more headroom, but you still aren't going to blow out the ears of the guy in the car next to you. IMO, an aftermarket amp is a waste. You can only move so much air with a little speaker. The darned laws of physics just get in the way. Volume just for the sake of volume is not an improvement. It's just loud.
Lastly, don't try to overpower all the noise you have on a bike. That is an exercise in futility. If you are like me and really like to use the external speakers, concentrate on improvements that make the riding position quieter. Fix what you have control over. Lowering noise levels makes as much of a difference in perceived volume as more power does. I also don't play music over about 45-50 mph. To me, it's pointless.
Get your audio sources leveled to the correct volume too. And limit your road music to simple tunes. Complex music that varies in volume level doesn't work well on a bike.
