Active Crossover Recommendations

Peter, I've fooled around a bit with active crossovers altho with no CURRENT products. I believe:
1. You'll find virtually no difference between any 3 adjacent frequencies in your string beginning at 70; they're just too close together. IOW, there's simply not enough difference between/among 100, 115, and 120, to pick just 3. The only 3 with enough split are the last 3.
2. I strongly recommend you use a single-order slope on the hi-pass filter to the Carys and that it be a 'passive active' filter, meaning no more than a series capacitor, and a VERY-high-quality one at that. Your Cary/988 backend is probably VERY resolving, and probably you'll hear the circuitry AND the additional cables AND all the additional connections if you use an active filter. Think about how many mechanical and solder connections you'd add to the signal path with an electronic crossover!
3. I suggest you use the lo-pass filter(s) in your powered subwoofer(s).
4. I suggest you use stereo subwoofers. There is indeed directionality to bass frequencies.

IMO what you need is a soldering iron, knowledge of your amp's input impedance, and a few hi-quality caps. I suggest you experiment with crossover frequencies (=cap values) using SoniCaps. When you've decided on a frequency/capacitance, replace the SoniCap with a SoniCap Platinum or AT LEAST a Cardas Golden Ratio, the 2 finest caps I've ever heard.

So...save your money by NOT buying an electronic crossover, experiment with cap values, and enjoy superior sound thru your system. BTW I think you'll end up with a LOTS-lower hi-pass crossover frequency than 100 and above.
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Jeffreybehr's suggestion is a good one if a 6dB high pass is OK, and for this application it is. However, I believe that a good electronics X/O would do the job without audible degradation.

My only caution is that this fixed capacitor approach does not give you flexibility to easily change the X/O frequency. I have recently concluded, after years of seeking the "right" frequency, that there is no "right" frequency for all music. So I have a X/O that is easily changed with the twist of a knob.

I am presently running a B&K PT-5, it has an 80hz low pass output, and a 100hz high pass output, and dual mono outputs, it works very well. However, certain amplifiers can tax this units power supply, and hence, it's output abilities, the sound however, is very good.

Wednsday I will recieve my Van Alstien Super Pas 3 tube preamp, it will be interesting to "hear" how tubes compare. I am running a pair of Cerwin Vega 15's for the low end, and Dynaudio/Vifa for the upper registers in a 14x28 room- spl has been mesured at over 140db at full power (given the source). Presently, amplification is two Proton D1200's, and an Audio refinement CD player.

I have experimented with a Crown 3-way active and it was very good, but the more you add the less you get (so to speak) this is why I chose the B&K, simple and yet, good sound for not much money.

Peter, I didn't go quite far enough in my comments. I believe that in a subwoofered system, one needs to run the main system as full-range as it and you can stand. With your 988s, I believe you'd increase their power-handling capacity substantially merely by removing most of the low bass from their signal. That can be done with a 40- or 50Hz hi-pass filter point; I'd start with a 50. Then set the woofers' crossover points and levels wherever you want that SOUNDS good. The point is to keep your fine-sounding main system doing about 90% of the work, and sounding GREAT at it, of course, while increasing power-handling a bit AND adding lo-bass capability. The trick will be to find PLACES for the woofers to blend well with the main system.

I've done something similar in biamping my Eminent Technology 8s. Initially I duplicated ET's c. 40Hz MR hi-pass filter point with an active filter in the amps. I then eliminated the hi-pass filter and have been running the MR panels wide open. I THINK it sounds better. At least I've eliminated the sound of one cap and its inherent phase errors.

If those 'Cary EL34 triode amps' are Rocket 88s, their 150K-Ohm input impedance would create a 48Hz filter with a 0.022µF cap.

Good luck. Pls let us know what you do.
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Peter,

Try Bryston 10B sub ccrossover with following settings..
High Pass 100 - 110Hz 18 DB slope
Low Pass 50Hz 18DB slope
+3 DB sub volume

or

just run quads full range and use crossover to roll off sub only around 40hz....volume maybe down 1-2db
Dan