Arriving Kansai Airport

We are arriving at Kansai Airport on Sunday 4th May at 21.00 hrs.I am looking for advice as to whether we will be able to change our JRPass vouchers into Passes and book train tickets at that time of night? Also which would be the best route to Osaka station(not Shin osaka)--the train of somesort or limousine bus at that time.We are staying at the Hilton Osaka for our first night. I have researched the site and variuos others but can't quite get it clear as it is Golden Week and things may be different from the norm.
Advice would be appreciated as always and everyones information makes trip planning so much more successful. thank you.

The Kansai airport office is open until 2300
The JR airport train requires one change or you can take the Kanku rapid to Osaka without a change but it takes around 70' The Kanku trains also run much later than do the dedicated airport Haruka services the last of which leaves at 2216.

The JR pass exchange counter at Kansai Airport Station is open until 11pm.
http://www.japanrailpass.net/eng/en009.html

The last bus to Umeda where your hotel is located leaves 23:15.
http://www.kate.co.jp/pc/e_time_table/e_osaka_sta_tt.html#fr...

Hope this helps.

Thank you both for the help that has made it so much clearer. I have printed off your answers and will take them with me.
Much appreciated.