I see the OP has 3 HR21-100's. If they put the 2-way splitters in between the DECA and the HR20's, those 3 BSF's won't be needed.
Looks to me like you'll need:
1- SWiM-16 + P.I.
6- DECA's + 1-DECA P.I. (5 HR's and the broadband connection)
1- 8way splitter (or 2- 4way's) to connect 6 DECA's to a SWiM-16
3- 2way splitters to connect your HR20-100's
Looking at the thread about connecting the HR20-100's, I see that the method that you suggest (without the BSF's) is not officially supported by Directv, but that it does work for most people. Should I insist that the installer put in the BSF's, or won't it really matter?
Since I have 5 DVR's (10 tuners), would I only need 1 8-way splitter (or 2 4-ways)? Is each output of a splitter capable of passing 2 tuners to each DVR in a SWiM setup?
Or, are you saying to get my 8 tuners from the 8-way, and the other 2 from the other SWiM-16 output?