The Xtreme head for the Solo PRO requires the linkage circled below.  Nine Eagles has changed the linkage for 2010.  If you do not currently have the linkage circled below, this head will not work with your existing linkage.  This linkage is no longer available from Nine Eagles, but ClubHeli has arranged custom linkage that can be purchased here: http://www.clubheli.com/Solo-PRO-Linkage-for-Xtreme-Head--JJetski_p_2758.html