I am in fabbing up twins right now I am taking off the hx 40 installing the stock hx35 with a hx55 secondary on the hx35 I am trying a 18cm housing first I have a 16cm and 21cm to try the 55 has a 22 housing with a 5inch outlet I bought new on ebay for 300 bucks. I am just wondering if any one has tried this combo or close to it . I will post as soon as its done with in 2 weeks I hope