I actually enjoy to read about the hardship that Steve Huffman went through when he heard the transformer buzz/hum from his over $10k Luxman and then found the Puritan 156 to finally tame it down. My Parasound amps have a bit transformer hum as well that I need to 2 ft close to hear it but is enough to trigger my irritation. I was doing the similar things, i.e., DC offset and Monster power conditioner, trying to get rid of it but without success. It is tempting but I could not justify spending $2k to cure the hum of $1k amp.
I found a used mPre selling for $700. Is it a fair price? It is such a pity that its DAC section only supports up to 24/96 (usb) and 24/192 and no DSD. Well, let me sleep on it.