Cable select only works with 80-conductor cable w/ 40-pin connector. If only one device on any cable, sometimes cable select will work. If 2 devices, use 40-conductor with master/slave and 80-conductor with cable select. 40-conductor cable only supports up to UDMA Mode 2 (UDMA-33). 80-conductor cable defaults to UDMA-33 if motherboard interface is only UDMA-33.
2 hard drives on one 80-conductor cable works just fine with cable select.
Use the cable that came with your new drive. It's probably 80-conductor.
Read this: http://www.pcguide.com/ref/hdd/if/ide/confCable80-c.html