Funny, I will be in your situation before long since I am getting a pair of MS4 to replace a Mentor 6 I am selling. I have the Helicon 800 mk II as well. I am running the Mentors on a Vincent 236 mk (hybrid tube) and the Helicon's on a Lyngdorf Millennium mkiv, both are 150 W. Of course these are easier to drive the the MS4 given the sensitivity. I recently contacted DALI regarding my set up and either of these amps; that is 150 W and/or hybrid amp. Their ideal recommendation was to bi amp the Euphonia's. Ok, so second best was to bi wire (which I do now with jumpers in one case and bi wire in the other) and to use an amp that can handle a 4 ohm load. I can tell you I will not change amps for hooking up the Euphonia's but then I do have the luxury of 2 amps in this system. My research tells me that if you stay at least in that W range you will be fine. The DALI's are known to be driven, and sound great, with tube gear, but you may opt for a hybrid since it may cost a fortune to get a very powerful tube amp, and frankly I do not trust the physics behind those who claim that tube power is twice SS power. In the past I have phoned DALI USA and asked to speak to a tech. I got a friendly, heavy accented Danish man that took all the time in the world to answer my questions. As I enjoyed our conversation drifting into Danish classical composers, little did he nor I know I would go on to keep buying up in their speaker line. If he is still here, his email is: mvj@dali.com Good luck and let me know what you find out, I am at rf.fenster@gmail.com