Power requirements for Vandersteen 3A Sig + 2Wq

If you used a powered sub with a full range speaker, and you roll-off the low end before amplification (as recommended for the 3A Sig + 2Wq marriage), does this mean you can get by with less power without impacting dynamics?

Would a CAD-808 (Rocket 88) be appropriate with this configuration?
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power requirements always depend on the room size, music you play, and how loud you like to play. With that said you CAN get buy with a smaller main amp. How small depends on the things I already mentioned. I use a 45 watt per channel tube amp with my 2Ce's(similar sensitivity) and my 2Wq and it works great for me in a mid size room, and will play louder that you should listen at times. I can tell you that the 88 and the 2Wq will play louder than just the 88 driving the 3's. (Here is a blatent plug for something I have for sale, mine are likely the wrong value for an amp with an input impedance of 105K ohms anyway)make sure that you at least get the fixed filters for the sub instead of the switchable unit that comes standard with the woofer.
From my own experience, I found that the 3A Sig's, when combined with a single 2Wq sub in a small to medium-sized room, can be driven with as little as 50 wpc, PROVIDED you don't listen at high SPL's. That said, I have found that my 3A Sig's work better for both audio and HT with at an amp that offers a clean 100-150 wpc (3-4 db increase, which improves the headroom dynamics).

My current system has 3A Sig's and a stereo pair of 2Wq's (which I find far superior to a single sub, not just for higher SPL's, but also for better audio quality). My 3A Sig's are powered by a Bryston 4B-ST amp (about 300 wpc), but I am confident that a 150 wpc amp would be more than sufficient in my medium-sized room. If you add a stereo pair of 2Wq's subs, and you don't listen at ear-bleed levels, then 100-150 wpc will normally be adequate to drive the 3A Sig's.

A closing thought about the 2Wq subs. I upgraded the crossovers for my 2Wq's to the X-overs made for the Vandy Model 5 speakers. These X-overs aren't cheap -- $600 for a single-ended pair (separate, stainless steel boxes for each channel) -- but they are virtually seamless, and a decided improvement over the standard fixed value crossover. The Model 5 crossovers have first-rate internal parts, and have dip switches that allow you to change the values should you get a new amp. Admittedly the Model 5 X-overs are icing on the cake, but certainly worth considering if the rest of your system merits them.

As I have commented before in this forum about the 3A Sig's when combined with the 2Wq subs, you not only get higher SPL's without distortion, but the mid-range clarity improves as well (Richard Vandersteen says this is due to the decreased IM distortion of the 3A Sig's drivers). The improved mid-range is a very nice "plus" from adding the 2Wq subs, but there is an "unintended consequence": a tendency to listen at higher levels because everything sounds so clean. This may necessitate a bit more amplifier power, so if you plan to add either 1 or 2 Vandy subs, you might be best advised to use an amp with a bit more power than the minimum you think you need.
Well, I too use the Vandersteen 3A Sigs and a pair of 2wq's. I have vertically biamped them using McCormack DNA .5 amps which are 100+ per ch. at 8 ohms. They double down and provide more than adequate power for anything but ear damaging levels. I have definitely concluded that vertical biamping is more transparent and better sounding than a single bi-wired amp.
The fun part came trying to get the high pass correct. I have not used the Model 5 crossover so I can't comment on that. However, I have used the fixed crossover. I found it to impart a slight veiling to the sound compared to being the circuit vs being out. Using the formula 1 divided by 2pi(6.28) x f(crossover freq.) x z(input impedance)to find the capacitance required, I have made my own filter plugged directly into the channel input for the bass on each amp using Infinicaps. The crossover is out of the amp channel driving the mids and highs. This provided transparent and seemless sound to a level I don't feel the need to change. I ran this by Richard Hardesty (Audioperfectionist) and this is what he has done also. He also said he would make a statement after his research if it was better to run all channels through the filter or just the bass. So we'll see what he says. My conclusion is this is the way to go.
Back to the original question of power, the 3A Sigs really need no less than 100 watts per side in my opinion even with the subs. I can say that they open up more with more power. That is why I'm anxious to try the Theta Dreadnaught with these speakers.