vanalstine fet valve amplifiers

In the world of amplifiers was wondering where the Vanalstine Fet Valve 350 and 550 fit in and do they need to pair up with a Vanalstine preamp to really sound their best?
Not really sure where they fit in, but the 550ex is a very nice hybrid for the money. Probably sound's it's best with a speaker design that doesn't reach for too much resolution (think soft dome tweeter, not ribbon)
It does need a Telefunken or other quality NOS tube to truly sound good.
I ran it with a Placette passive preamp and really enjoyed the setup. So, no it doesn't need a Van Alstine pre.
Highly recommended at the used price's.
I use a Primare pre with mine. Sound is excellent.
I ran mine with Platinum Audio Solo and Audio Physic Avanti Century III speakers and it sounded really good.

I subsequently had the amp modified to balanced outputs and upgraded wiring and internal parts (Jospeh Chow, Audio Horizions)and that took it to another level. The pre-amp I've mostly used with it has been a heavily modified tube Air Tight.

Right now I use this amp in a biamp configuration driving the bass drivers of Emerald Physic speakers. Same pre-amp and the sound is excellent.
Appreciate the responses. Gives me some good options to think about.
My Ultra 550 is paired with a Malpetree Audio 2A SE and driving my soft-dome tweetered EgglestonWroks Fontaines. The sound is clear and well-balanced top to bottom. Very powerful with no distortion. I have upraded tubes in both the amp and pre to my liking (fuller sound).