If you just want XM and have a method of amplification on your motorcycle, Harley Davidson makes a superb, waterproof, large button (easy for gloves) XM unit.
My wife had one on her FJR for 100k and it was never a problem. I just gave it to a friend the other day for thier boat.
I always thought it was hilarious o see the HD radio on the handlebars
Link
http://www.google.com/products/catalog?hl=en&sugexp=gsis,i18n%3Dtrue&cp=17&gs_id=2o&xhr=t&q=harley+davidson+xm+radio&pq=louis+ck&biw=1024&bih=660&gs_upl=&bav=on.2,or.r_gc.r_pw.&um=1&ie=UTF-8&tbm=shop&cid=7485123814201524023&sa=X&ei=om5vTqfcM4PYiAKCsfWPBw&sqi=2&ved=0CC0Q8wIwAQ
Some folks don't want a gps but want music and this unit is excellent for them
