Hi Match...; I bi-amped the Vand. 3Asigs with a pair of McCormack DNA 2 Rev As, and could not honestly tell the difference between one amp and two (but initially I CONVINCED myself that I could-- bad mistake). But then the DNA2 is a very powerful amp (300 wpc 8 Ohm) to begin with.
I'm with the guys who responded above, if you like the 3Asigs, they are excellent speakers, and subs will improve them much more than bi-amping. Bi-wiring, as Vandersteen recommends, is worthwhile. Just use a good quality 200 wpc (or so) amp that you like (I used a McCormack DNA-1 Dlx with excellent results), and you'll be happy. The 3Asigs are wonderful speakers even without subs too. Cheers. Craig