Pass Labs xa - .5 amps

Rabbani, your choice of speakers will depend on your room size. I'd suggest anything 90+ dB given a small or medium size room. A large room would require a more sensitive speaker.

Impedance curve characteristics are of less importance since the XA-.5 series amps double power as speaker impedance is halved.

However, IMO, you should choose speakers before selecting an amp. Having done it the other way around, I realize what a mistake it is.

To be more exact, the result was a tonal imbalance with the highs louder than the bass and midbass, resulting in a tipped up or bright sound. The tube amps used were VAC MusicBloc 160 push pull and Atma-Sphere M-60 OTL.

Physically that might be explained by the higher output impedance of the tube amps. As output impedance nears that of the speaker then you will modulate the amount of voltage reaching the voice coil by the variation of the speaker impedance with frequency. For example, if the amp has an output impedance of 4 ohms then where the impedance of the speaker drops to 4 ohms you will get roughly half the voltage at the voice coil than you get at a point where the speaker impedance rises to 40 ohms (at 4 ohms half the voltage is dropped across the output of the amp while at 40 ohms only 10% is dropped). Obviously, if the speaker has been designed to be flat in frequency response when driven by an SS amp then you will hear a "tilted" presentation when played with a higher output impedance tube amp.

I am sure Tvad knows this very well - having directly experienced it and based on all his other knowledgeable posts here on Audiogon. So my comments are simply intended for those who are puzzled as to the cause of Tvad's observations...that's all.

Shadorne, you nailed it. Basically, the tube amps produce varying decibel levels across the frequency band, with the higher frequencies (and the higher impedances) generally having higher decibel levels relative to the lower frequencies (and the lower impedances).

There are several Sonata III owners who happily use tube amps, so it seems we are not all equally sensitive to tonal imbalance.

Tvad, I was doing a search on the silverlines, (I've always wanted to hear them) and I saw several mentions where Alan Yun preferred tube amps. It might have been for a different model. Regardless, it sounds like you've sorted it out to your liking, and after all said and done that's the important part.
Just because the Pass gear didn't work for us doesn't mean it won't for somebody else. My new mantra: Listen for yourselves, people!

06-04-09: Chashas1
Tvad, I was doing a search on the silverlines, (I've always wanted to hear them) and I saw several mentions where Alan Yun preferred tube amps.

I attended two CES shows (2004 and 2005), and one LA audio show (2005, I think...) at which Alan demonstrated his speakers with a Pass Labs XA-600 amplifier. He also had a Silverline 300B tube amp available if anyone wanted to hear his speakers driven by tubes.

During discussions with Alan, he told me he voices his speakers with Pass Labs, and it was during one of those conversations that he recommended Pass Labs as an optimal match for the Sonata III speakers when I mentioned my concern about a perceived brightness in the speakers. He also mentioned Belles amps as a less expensive alternative.