Hey John, welcome and IMO save your time and $'s. There is no way you are going to be able to get the kind of sound you are used to on your Harley from the Trophy. The new Harleys have a kick ass sound system. First the speaker box / space in the dash of the trophy is too small and as far as rear speakers you would need to build rear speaker boxes on the rear foot pegs or invest in a totally custom top case.
You may want to consider ear buds instead and or helmet based speakers. I know your thoughts on helmet but they do provide excellent audio. :>)
You can modify some earbuds for headphone quality audio. I don't recommend the headphones on the bike. They'll get you stopped immediately in almost any jurisdiction. Following is an earbud mod you may consider.
I use the following config for jogging & cycling in the park and recommend it for cycling as well. I have a set of Monster Cable Earth Wind and Fire Gratitude In-ear Headphones
http://www.amazon.com/Monster-Cable-Gratitude-In-ear-Headphones/dp/B0057X4TWA and I did not pay that much. With the buds removed they have a transducer with about a 3/16th's end piece for fitment of their assorted ear pieces. I found their assortment of foamies adequate but not great.
Step one is to apply some electrical heat shrink wrap to the transducer cylinder. Step two is to build a channel for the shrink tube and sound to travel thru the ear plug. Blowtorch / heat a nail to red hot and melt a path thru the earplug. Step three insert transducer with shrink tube into the still warm and sticky ear plug. No hurry the melted earplug material has a tendency to remain sticky for some time and will adhere to the shrink wrap tunnel. Moisten foam and stuff into ear canal.
Here lies the important info. The earplugs I use are Moldex "NASCAR" branded and have a NRR of 33. [Don't care about NASCAR but it is the highest NRR I've found in a foamy.
http://www.amazon.com/Moldex-Disposable-Earplugs-Uncorded-Officially/dp/B00SW15K1S/ref=sr_1_4?s=electronics&ie=UTF8&qid=1447178663&sr=8-4&keywords=moldex+nascar [Did not pay that much :>)]
This combo will virtually eliminate all outside noise and are hence a danger to you and others. My config for jogging and bicycle is: insert right ear plug only and the music files I listen to has been modified to magnificent mono. The ambient noise reduction is significant and much better than you get from any stock earbud config. Sound is great. I have left ear open so I can retain touch with my environment. Lesser NRR earplugs will improve spacial awareness and the NRR factor does reduce over time. There is still one issue to overcome and how you accomplish that is up to you and dependent on your bikes config. The wind will whip the leads from your iPhone / iPod / iSource to a degree depending on windscreen and the leads will transmit unwanted sound of cord thump to the bud. That part of the fix I will leave to individual user. Having device in jacket or T-Shirt and leads up a t-shirt etc will help.
YMMV and no warranty expressed or implied. Employ this methodology at your own risk. I am confident it is illegal as well in every state but I'm sure it is harder to detect than a set of earphones.
Best of luck
Studley