If the target is a high growth company and its growth is attributed to advanced technological systems that it uses, refined business processes and highly flexible work environment, how difficult it gets to integrate it in a parent company which still uses legacy technological systems and business processes and has matrixed organization structure?
If you integrade a company as described into one with older technologies/traditions, you will lose technological advancement, taltented IT people who will not work with old technology, experts/families who rely on flexible working hours, etc. So there are two options: keep the separate or try to modernize the acquiring company.
As the target co. is using much superior technology/processes than the acquiring company, the best option would be to adopt to target company systems/processes/procedures and ensure to retain all the target company employees who are driving it. The difficult part is acquiring co. employees would not be happy about it and start to leave the company which the management accept it.