Definitely agree with both Vetterone and Cello, the Berning ZH270 is an outstanding choice for your system. The Berning ZH270 and Merlin combination is near legendary (as a quick search of the archives here on Audiogon will attest).
Furthemore, the Berning ZH270 will allow you to run your modified Wadia 850 directly into the amplifier, since the ZH270 has two sets of switchable inputs plus an internal volume control. There is no preamp, quite like no preamp, regardless of cost. Furthermore, running the Wadia direct will remove a complete set of cables and jacks from your system further enhancing the transparency: you will hear musical details on your recordings that will surprise you.
As for the overall sound, the Berning is the most detailed and transparent amplifier I have owned. Relative to conventional transformer-coupled tube amplifiers based on the common 6550/KT88 or EL34/KT77 power tube families, the Berning ZH270 is more dynamic, more detailed, AND more musical. Relative to conventional OTL amplifiers, which run many output tubes in parallel in an attempt to provide enough current to drive even medium efficiency speakers, the Berning ZH270 is faster, more accurate, and delivers deep well-controlled bass.
After listening to the Berning ZH270, you quickly come to realize that both the conventional transformer-coupled tube amplifiers and the conventional OTL tube amplifiers are design compromises when used with real world speakers. Given that many serious speaker manufacturers -- including Merlin -- use the ZH270 to evaluate their speakers, there is a truth to the statement that "you have not really heard what your speakers are fully capable of until you hear them driven by a Berning ZH270".
If you need more power than a single Berning ZH270 can deliver, then two Berning ZH270 amplifiers wired as monoblocks or wired for vertical bi-amping is a sonic revelation.
If you are new to tubes, the Berning has several key features that make it much more user friendly than most tube amplifiers. The Berning ZH270 runs cool compared to nearly all other tube amplifiers (and even many solid state amplifiers). The Berning ZH270 autobiases all of its tubes/triode sections independently, so there is no bias to adjust. The tubes are also biased for low idle current so they will last a long, long time. Other cutting edge features include heating all of the tubes with radio frequency AC, rather than using DC. In most amplifiers, the DC used to heat the tubes is often accompanied with small amounts of 120 Hz ripple, resulting in subtle distortion or even a slight hum. By contrast, the ZH270 the quietest tube amplifier I have owned.
As for cost, even with all of the modifications offered by Allan Bhagan (info@zotl.com) such as upgraded capacitors, silver wire in the signal path, and matched cryo-treated output tubes (all highly recommended mods), the Berning ZH270 is an incredible value.
