Z-Systems RDP-1 and RDQ-1

Does anyone out there have experience with these units? What are you impressions? Are they really as great as the reviews say they are? Is it really effective to use the RDP-1 as a preamp. i.e. going straight from the DAC into the power amp? Any drawbacks to this, aside from problems with analog sources? Your shared wisdom and experience would be appreciated.
I am currentlly using the Z-systems RDP-1 as a preamp going into a DAC which is then fed into two SET VAIC 52B mono-block amplifiers (O dB negative feedback, 100 Kohms input impedance, 35 Watt output power). I have detected no drawbacks whatsoever from this set-up, only advantages (elimination of analog preamp grunge, cut-down on analog interconnect coloration, and the use of the extremely precise "transparent tone control" EQ for boosting extreme lows and highs, which tend to roll of with tube amps, some cartridges, etc. and for room correction and for the occassional experimentation with selective coloration and re-EQing). Your post implies that there would be problems with analog sources, but I have not had any (except that analog source are far more difficult to EQ satisfactorily than digital sources, and that a high-quality cartridge and phonostage makes things easier with the Z-system). Right now, I run a Simon Yorke turntable with a Transfiguration Temper Supreme through a phono stage (I have a few different ones, both tube and solid-state) into the radc-2 analog to digital convertor and then into the RDP-1. The RDP-1 has always operated flawlessly, and the digital volume control is--again--transparent (it is usually turned to between -40dB to -18dB with this setup, depending on the source). One thing I have learned over the year I have been using it is that the Z-Systems digital preamp responds very strongly to the benefits of a good power cable (too bad that the tiny radc-2 ADC has just a wall-wart transformer), and that the best thing to do is to use high-quality matching power cables on your Z-Systems and whatever DAC your are using. I have been using NBS cables with superb results on the Z-System. You do not have to invest very much in expensive digital cables (but the AES/EBU input is a tick better than the other inputs), but invest in power cables and--above all else--the analog cable betweent the DAC and the power amps. I have read many raves about the Z-systems and have found little that is unfounded.
Sleeping on this post, I thought I should include two areas for improvement in the Z-systems equipment.
1. Find a better way of powering the radc-2 than a wall-wart. I will probably throw out the stock power supply soon for a high-quality stand-alone power supply soon. Otherwise, all you can do is use line filters (with audible improvements in performance, still).
2. I cannot believe that the "bypass mode" of the RDP-1 is a true bypass. There seems to be some influence from the RDP-1 even in bypass. I think that this issue, however, has already been addressed by Z-systems and that they modified the power supply of the RDP-1 to overcome this problem a year ago.
Last note: I am one of those listeners who dislike the removal of tone controls and phono stages from high-quality preamps, and I have found the Z-systems to be the best way for adding precise tone control to a system. (I would never want to use a cheap 7 or 12 or whatever band analog graphic equalizer, and the only analog preamp tone control system that I have heard that equals and even excells the Z-systems is the Cello Audio Palette) Whenever I do a blind-fold test with guests, they prefer the EQ settings I have developed for different recordings over the direct signal. After my experiences with recording studio equalization (I have been a client at different 8, 24, 32 track recording studios in the NYC area and in Europe), I could not live at home without EQ on my system. The Z-systems RDP-1 has allowed me to bring a part of the recording studio into my home playback system, and has given me many hours of pleasure. This is starting to sound like advertising copy, so I am signing off. Happy auditioning Bswillia.