Experience with Audio Research SDP-1

Looking for anyone with experience, pro or con, with using the Audio Research SDP-1. The SDP-1 was Audio Research's attempt at pseudo-surround sound. It synthesized rear and center surround channels and was available in the mid to late 90's. I borrowed one from a fellow audiophile and have had mixed results. When the source material is right it sounds good, but with some material the rear surrounds (I'm not using the center channel) have what sounds like a high distortion level. This is especially noticeable when playing a mono source. While the sound is intriguing, the occasional distortion and added complexity to the system makes me cringe!
You might want to check with ARC support. I believe the device required a stereo signal to work at all.
Personally, I'd leave it alone. 5.1 + systems are great for video and 2 channel can take you all the way there for audio. The SDP-1 unit is akwardly in the middle.
I disagree with Brauser. The SDP1 is a great product for driving a pair of rear speakers for audio only. I would not want a HT preamp/processor to botch up what I worked so hard to attain for my front channels. And the rear channels with the SPD1 make for an incredible listening experience. I never did try with a center speaker.

Due to the changes in my room and system, I will soon part ways with my SPD1 but it has been a wonderful product.

Four years after this short thread started, I aquired and am now enjoying an ARC SDP-1. I am strictly a 2-channel audio enthusiast: LP records, Vacuum tubes and electrostats. But adding 2 more channels of delayed sound did increase the realism of my system. Just adding the SDP-1, 2 small rear channel speakers (Athena), and an Amber amp (that I've had for 15 years) made a dramatic improvement in the realistic presentation of a live event in my living room. I cannot detect any degradation, only improvement.
There was a newer chip used in later versions of the SDP1 which made the unit much quieter. Older units can be sent in to ARC for an upgrade. Also, leaving the unit on at all times makes it noticeably quieter and also better sounding.

The SDP1 is an excellent and non-intrusive piece that can be added to the highest end systems for extracting the out-of-phase ambient information that is contained on good stereo recordings and naturally presenting that information through a pair of rear speakers. An optional center channel can also be connected. The SDP1 does NOT get introduced into the signal path of your front channels in any way and can be engaged and disengaged (returning you to your original two channel system) at the flip of a switch.

I can understand why some who have never heard one properly set up would doubt the need for such a device, but I can tell you that the results are truly amazing. It does require some pretty good cables, amplification, and rear channel speakers in order to avoid degrading the sound of your main front channels.

When properly set up and dialed in, the listener will have no idea that rear speakers are making any sound come from behind them, but will experience a much more three-dimensional front stage, richer harmonics, better decay, and a sense that they are breathing the same air as the performers rather than looking in a performance from the outside.

Very cool product.
Now it has been three more years. I am still listening to the SDP-1 in my high-end audio system, and really like it. I have upgraded the dedicated rear amplifier to an Audio Research solid-state model that I picked-up for a good price. And I upgraded the rear speakers to ERA Design-4. But I am really not sure these upgrades made any difference. The rear channels are so subtle, that I really have no awareness of them, other than the soundstage being larger and more convincing. So, the satisfaction from this SDP-1 continues, even after many years.