I guess the main problem is that the device can only be used with a system totally designed for active use, with seperate amps for each speaker driver, and the crossover points set for a particular speaker system.
I normally use a DEQX digital crossover on my two-way active electrostatic speakers and the versatility of the DEQX is quite useful- I have 3 crossover settings, EQ available via remote control, and can change settings on the fly to suit taste and recordings etc.
The DEQX is very transparent and with tube preamp and tube amps designed for the stats the sound is accurate and natural.
But if you crave an all tube system, and know what crossover settings your speakers need, a tube active crossover can give very good results. With a two way system it is quite easy to go up to 24dB fourth order slopes with tubes, combine a very good preamp in the design and have an exceptionally satisfying sound with all tube pre/active amplification.
Kevin Covi did a lot of crossover design work for me in 2006 and I built quite a few preamp/crossover units for those dedicated audiophiles with a passion for tubes.
Another advantage of combining the preamp and crossover is that the unit can be optimised for the range of frequencies each section covers.
In the pre/crossover I'm using now I have 6SN7/6H30 tubes in White Follower configuration driving the bass section. This is optimised to give very deep, tight bass response.
The mid/treble uses a 6SN7/101D (dht) transformer coupled circuit which is optimised for performance from 200Hz. Normally I use a 71A dht for my preamps as it has the best balance for overall sound, but the 101D is maybe the best tube for clarity and is ideal from lower midrange up to high treble.
With this setup and using a bit of EQ via the JRiver player program the sound is perhaps not as precise and accurate as the DEQX but it sounds wonderfully engaging and musical.
On the pix above the middle front tubes are the bass section, and the round 101D tube handles the mid/treble. There is a seperate volume control for the bass which works in combination with the master volume control.
