Can always take the direct connect A-style backplane and just connect a sas3 HBA to the backplane and use sas3 disks, think it negotiates properly. Guess I could check, I have that same exact setup. :-D
EDIT: Yep my sas3 disks look good in that A-style direct connect scenario. (da1-4, husmm1680 connected to a LSI 9300-8i on a SC216 w/ A-style backplane) :-D
[root@freenas-esxi6a] /mnt/datazilla/tv_shows# dmesg | grep -i transfers
da0: 320.000MB/s transfers (160.000MHz DT, offset 127, 16bit)
da1: 1200.000MB/s transfers
da2: 1200.000MB/s transfers
da3: 1200.000MB/s transfers
da4: 1200.000MB/s transfers
da11: 600.000MB/s transfers
da12: 600.000MB/s transfers
da5: 600.000MB/s transfers
da8: 600.000MB/s transfers
da7: 600.000MB/s transfers
da6: 600.000MB/s transfers
da9: 600.000MB/s transfers
da10: 600.000MB/s transfers
cd0: 33.300MB/s transfers (UDMA2, ATAPI 12bytes, PIO 65534bytes)
[root@freenas-esxi6a] /mnt/datazilla/tv_shows# dmesg | grep -i gbps
mpr0: Found device <c01<SspTarg,Direct>,End Device> <12.0Gbps> handle<0x0009> enclosureHandle<0x0001> slot 7
mpr0: Found device <c01<SspTarg,Direct>,End Device> <12.0Gbps> handle<0x000a> enclosureHandle<0x0001> slot 6
mpr0: Found device <c01<SspTarg,Direct>,End Device> <12.0Gbps> handle<0x000b> enclosureHandle<0x0001> slot 4
mpr0: Found device <c01<SspTarg,Direct>,End Device> <12.0Gbps> handle<0x000c> enclosureHandle<0x0001> slot 5