5.5 width wheel are designed for 180 tires, 6.0 width are designed for 190. Can you stick a 190 on a 5.5, yes. Will it affect how you bike rides and corners, yes! the arch of the tire changes, thus the contact patch changes and also affects your flickablility of the bike. Most guru's in the bike world dont advise running a 190 on a 5.5.
I don't know where you live or what bike you ride, but there was a guy in San Francisco that had a pair of wheels for sale cheap a while back. he may still have them, if you have a single sided swing arm look on the BARF forum under parts and do a search for Ducati. Bay Area Riders Forum