What intrigues me about your question is why you seek a 300-400 watt/channel amp at all. Do you run your speakers in a huge room, or listen almost exclusively to big orchestral music or pounding pop/rock? Compared to a lower powered amp in the same line, high-powered amps are generally (i) more expensive, (ii) more complex and thus more likely to break, (iii) burn more electricity, (iv) are heavier and thus a pain in the ass to ship or move, and (v) most importantly, have a comparatively congested, less natural sound (lower powered amps, be they transistor or tube, have fewer output devices to muck up the sound). Unless you have an unusual need for power, e.g., super inefficient speakers, you are obsessed with Mahler symphonies or listen to Live at Leeds three times a week, you should consider going with a really high quality 100-150 watt/channel amp instead. If you buy carefully, the power supplies will be as good or better than a similarly priced amp having twice the wattage, making it sound subjectively very powerful, yet it will give you the finesse and musicality that almost no high wattage amp has. Also, do not rule out exceptional used products known for their build quality. For example, very few current production amps, regardless of their price, have the build quality and finesse of Rowland's Model 2 or Model 6 amps run from the Rowland battery power supplies -- those things will still be making music when a lot of the new amps mentioned in this thread will be dead and gone, and you'll have money left over for other things.