I understand I'm not going to get the sound like you would in a car or truck. But just wondering if there is another way to make it a bit louder at least without speakers distorting. I was wondering if 8 ohm 4 inch speakers would change that our do nothing at all
If you block the lowest frequencies from the speakers, they won't distort as much. Don't use the Loudness or bass control to boost frequencies the speakers can't reproduce and it will be better.
If you play it so loud that it distorts badly (you're not cranking it wide open, are you?), how well can you hear other drivers and people? I know wind noise and possibly a helmet block a lot of sounds from getting to your ears, but if it needs to be that loud (and, from other drivers' perspective, annoying), maybe a smart phone or iPod and Bluetooth headphones would be a better choice. It will sound better and it won't blare distorted noise.
I have heard very few motorcycles with anything that approaches decent sound and by the time it's loud enough for the rider to hear, it's just pissing off other people.
The main effect from 8 Ohm speakers is that you'll go from 25W (very optimistically rated) to about 12W- the reason vehicles use 4 Ohm speakers is due to the limited power supply voltage.
Post a photo of the bike- if the faring has enough space, you might be able to make a fiberglass enclosure for the speakers or some kind of pod- that can help.