In the MDA series of amplifiers, you would commonly find the MDA-300 and MDA-500 come up for sale… occasionally. What you would never find or maybe once in a blue, blue moon, is a pair of MDA-600s coming up for sale (only one pair has ever appeared for sale in the used market as far as we know). Being that only two pairs were ever made – One pair for Fabio and the other pair for Dan D’Agostino himself, good luck with ever finding another pair for sale. What is even rarer than the MDA-600s is this pair of MDA-400s that Dan specially built for a long time friend of his. This could be the only pair in the World (as far as we know)! And is probably even rarer than digging up a red diamond. Only the MDA-600s and this MDA-400s has the blue power output meter on its front that are similar to the uber high end KAS amplifiers. The MDA-300 and MDA-500 do not have them. Sonically, these are true high end reference amplifiers. Just fifteen minutes of listening got our hearts palpitating. The amount of “force” gushing out to the speakers are breathtaking. Its like unleashing the Niagara falls on to your speakers. If you currently own speakers that cost within the vicinity of $25,000, you may need to look further up down the road to properly pair the right speakers to these amps. That is how “over the top” these amps are. In our listening sessions, we barely moved the meters on the amps pass 30W and this was at ear popping levels (your experience may vary with your speakers and room). That was how dynamic these amps were. And if we were not in the business of selling hifi gears, we would have kept them for eternity. Cosmetically, the amps look really good. Like we mentioned above, they had one owner since it left Krell’s factory many, many years ago and was in a very simple but highly effective Krell setup where it was just a KPS-20iL, the MDA-400s and a pair of Avalon Radian HC speakers. Because of its rarity, we spared no expense in getting them back to its original spec through Krell’s authorized service center in NYC. It was re-capped, biased, worn out resistors and parts replaced etc etc. We don’t have the original boxes but due to its size and weight, they will have to ship freight, strapped on a pallet to arrive safely.