| Your not getting much help on this one are ya? Let me see if I can help.
I think we are a little confused by your question. I own a Road King and all the "slip-ons" I have ever seen don't have a cross over. But if you have a softtail and the pipes are together on the right side maybe some would.
Typically having a crossover is a good thing for low end power and smoothness. The best way is 2 into 1 for best power.
Now on the issue of sound.. it probably will sound different but I don't think it will make that much difference. If you want to be loud then you have to remove some of the back pressure such as open pipes. When you do that your power suffers on the low end.
Keep asking, because everyone has opinions when it comes to exhaust pipes. | 
