If you have an HSBC Merchant account there are a variety of choices to integrate payments with TourCMS
Global Iris is a 6 year deal, announced February 2012, using HSBC Merchant accounts with the Realex payment system. See announcement by HSBC / Realex. This is a new system and replaces the previous HSBC CPI Cardholder Payment Interface system.
Integrate as if you are integrating Realex payments into TourCMS. See the TourCMS Realex documentation
You can give your HSBC Merchant account details to Payment Express. They will charge you an additional monthly fee HOWEVER one advantage is that you can charge a saved credit card (ideal for tailor-made bookings where the final sale price is not known upfront)
As an alternative you can take your HSBC Merchant account details to Realex. The monthly fee is less than for Payment Express BUT you don't get the capability to charge saved credit cards (via TourCMS)