I also installed the Top Speed Cat delete pipes on my Boxster after I replaced my FDM exhaust with a PSE. The PSE was to quiet for me. Based on Kram's (KRAM36) recommendation (I miss him) I used EasySeal Exhaust Clamps.
EasySeal Exhaust Clamps: Torca EasySeal Clamps in Stainless Steel for Lap Joint Connections
As far as JayG's concern regarding deleting an emission component it is a fair topic to be discussed. During my searches on the topic I found that the Boxsters with the Top Speed cat delete pipes would still pass a smog test where a sniffer was used. I appears that the upstream cats are efficient enough to keep the emissions within compliance. You will fail a visual inspection though.