How Much Power Do Vandersteen 5a's Really Need?

Tomic, thanks very much for taking the time to explain things. It's greatly appreciated. I already have the impedance of my CJ in hand ( Input Impedance 100 kOhms).And I can understand the benefits of the external hi pass filters being employed.

However, I still cannot understand how the internal 5a bass amplifiers get a signal so that they are aware of what to reproduce. The information associated with the music being played is sent from the preamp to the M5HP's, and those then connect directly to the amplifier sending the music signal information to the amplifier, which then provides it to the speakers. Do the speaker connections on the 5a's internally distribute the amplified signal to both the bass amplifiers (for the bass signals), and separately to the midrange and tweeters?  

yes ! The internal amp in the 5a accepts a filtered speaker level input

right from your power amp. Now that you know amp input impedence, remove covers and set DIP switches to match settings called out in manual or on stickers affixed to each filter.

The high pass filter reduces the lows at a specific rate, but the lows are increased at the same rate which gives a flat frequency response.

I made the 5 hour drive (each way, not counting gas and food) to pick up the speakers today and all went well. VERY excited to have them home tonight with me. Beautiful Bubinga wood on these. And the surface is textured, a sort of crinkling that even adds to the look. 

Granted, after a brief glance at the manual (it has been a very long day) and all the previous comments, the setup on these seems pretty daunting. And I say that a someone who has successfully assisted and or set up at least a dozen speakers, of numerous brands, in the past. 

Getting everything locked down and optimized looks like  serious challenge, but, also clearly worth it in the end. 

Thanks to everyone for the explanations and assistance thus far in the process. Now I just have to wait for the single ended M5HP external high pass filters to arrive from Switzerland. I had to order them, as my equipment is single ended, and the speakers I purchased came with the XLR versions of the M5HP. Hopefully I can sell that and recoup that additional expense. I also need to quickly get in an order for the appropriate length of bi-wired cables, as I have nothing the right length, and every speaker I have is either terminated in bananas or spades too large to fit the terminal connections on the back of the 6a's. So, much as it will be painful, there will be a substantial delay before I can even start on this. :(