Passive high pass filter - Marchand XM446XLR-A

So, I am about to set up a new pair of monitor speakers and fill in the lower frequencies with two subs.  The monitors are Aerial LR5s and the subs will be two Aerial SW12s with internal 400 wpc amps.  The LR5s weigh 105 pounds each and play flat to just a bit above 40Hz (-6dB at 35Hz).  The Aerial subs are fast, powerful and musical and should integrate well with the LR5s.  My pre and power amps are solid state, fully balanced and the power amps provide 300/600 wpc into 8/4 ohms.  I will be running separate ICs from the preamp to my power amps and a second set from the preamp to the input on the subs.

My first question is whether I would benefit from using a high pass filter between the preamp and amplifiers to limit the low frequencies going to the LR5s so the amps are not trying to drive them full range.  

I didn't find a DIY design that I was comfortable with but I did run across several posts by people using a Marchand passive high pass filter.  The Marchand XM446XLR-A is fully balanced and has a high pass corner frequency of 80Hz (i.e., the frequency that is down by 3dB).  The Marchand has a standard slope of 24dB/octave but can be made for other slopes.

My second question is whether anyone out there has experience with the Marchand passive high pass filter and is it sufficiently transparent or should I expect to hear unwanted artifacts with the filter in my system?  

Finally, is there a higher quality alternative or should I simply play with the low pass on the sub and forget about filtering the signal to the main speakers?
drop me a note if you'd like to experiment - i have a marchand that didn't leave when i sold my subs.
The Marchand crossovers are very well regarded in the hardcore DIY community. The maker can supply the owner replaceable "cards" to insert in the x/o, providing just about any x/o frequency and slope one desires. And most are available with balanced XLR jacks, unlike the similarly-priced First Watt B4, another fine unit. The B4, unlike the Marchands, contains no Opamps, achieving filtering via all discrete parts. The B4 also needs no extra-cost filter cards, having internal dip-switches to set frequency and slope characteristics.
Thanks guys for the responses so far.  bdp24, I believe you are talking about Marchand's active crossovers but I am not interested in putting another active component in the signal chain.  Thank you for referencing the First Watt B4.  Even though it is an active device, it was still interesting to read the manuals by Pass.  It would be interesting ot me if he would offer a passive kit that the user could stuff with their favorite caps and resistors, and to provide some technical information on component compatibility and matching subs to the main speakers.

I have not yet read anything saying the Marchand passive high pass filter is exceptional, or does nothing unwanted to the signal.  Instead, what I have mostly read is that some prefer the Marchand high pass to doing nothing because they believe reducing the demand for the main amplifier to drive low frequencies improves clarity in the upper frequency ranges.  The flavor of most of the posts seems to be that one way or the other is a lesser of two evils.

I am really interested in hearing from folks with a high end and resolving system who are using monitor type main speakers mated with subs, and the method they have found to best cross over the subs to the mains.

One advantage I have is that my subs and main speakers come from the same manufacturer and are made to work together.  There is an option to use a crossover within the subs to high pass the main signal so that is something else I can at least try, particularly if I position the subs near the main speakers so the second IC from the subs to the mains would be short.

Now that I have finally received the main speakers, second sub and stands for everything, I will contact the manufacturer to verify their recommendation for the best way to integrate the high and low frequencies.  Would still appreciate hearing about success stories.