I'm glad you called D-Sonic, you probably talked to the owner, Dennis Deacon. He's a good guy to talk to, very knowledgeable about amps, speakers and good combinations of both.
I think the guy you're talking about who mods Magnepans calls himself Peter Gunn. I think this is just the name he adopted for his business because his last name is Polish and hard to pronounce and remember. Woodworker clients know him as John Henry and audiophiles know him as Peter Gunn His real first name is John but I'm not sure of his real last name. Confusing, right?
I'm not surprised he's recommending D-Sonic amps to his customers. He's been modding Magnepans for years and if anyone knows about good amps to mate with them, it would be him.
He's a woodworker and an audiophile who has a company called Magnestand. Here's a link: http://www.indiespinzone.com/mag/mag5.html
Sorry, I've read some of his posts on various audio websites but have never used his mod services and haven't read his comments yet about the .7 models. Please let me know the link and I'll check out his comments.
You asked: "What pre amp would work well these you think?"
A critical factor in matching preamps to amps is properly matching the preamp's Output Impedance to the amp's Input Impedance. Ideally for best matching and performance, an amp's Input Impedance should be at least 10 times higher than the preamp's Output Impedance. Since the D-Sonic M3-1500-M amp's Input Impedance is 60,000 ohms, the preamp you use should have an Output Impedance of 6,000 ohms or less (6,000 times 10 equals 60,000). In other words, if you decide to buy the D-Sonic amps, just make sure the preamp you select has an Output Impedance of 6,000 or less and it will work optimally.
Another great attribute of the D-Sonic M3-1500-M amps is their neutral sonic character that allows them to perform as the often cited amplifier ideal of a 'straight wire with gain' which is defined as taking the inputted signal and amplifying it faithfully without adding, subtracting or altering anything to this signal before sending the amplified signal to the speakers.
Due to the extraordinarily neutral quality of these amps, the result is that the sonic qualities of the preamp will be a greater determinant of the system's sound than it would be if less neutral amps were used.
This also means that the preamp you choose must be done carefully since it's going to largely determine, along with the sonic qualities of your other upstream source components, the overall sonic qualities of your system. My D-Sonic amps share this neutral quality and I find it much easier to detect the sonic affects of any changes in upstream components and even smaller changes such as speaker cables, interconnects and power cords than it was when I previously used a class A/B amp.
w Unfortunately, Without knowing more about the overall system sonic qualities you prefer, I don't feel I can give you specific preamp recommendations that would be useful to you. Until you let me know your overall system sonic preferences, however, I will offer some general guidelines:
If you prefer an accurate and neutral system sound, I would suggest you audition solid-state preamps that have an Output Impedance of 6,000 ohms or less.
If you prefer a more colored system sound that is on the warmer side of neutral, I would suggest you audition tubed preamps that have an Output Impedance of 6,00 ohms or less.
Once you inform me of your system sonic preferences and an estimated budget for a preamp, I can give you much more specific preamp options.