Best Power amps in $7000 range

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.

The advice given by other posters about using your budget to upgrade other parts of your system at the same time you buy an amp is sound, especially given your speakers. I checked out your Ushers. Fine speakers, but output limited with two midbass drivers and no dedicated woofers. If rock is what you mostly listen to, you need a high output speaker.

Ideally, you should consider horns or powered speakers like ATC or Genelec. Assuming you are not ready for that, however, I would look at a pair of used Vienna Acoustic Mahlers (+/- $4,500 for a mint used pair). They are 90 db. efficient and each speaker uses the same two 7" midbass drivers as the Wilson Maxx II, plus two 10" woofer, all with ported bass loading -- they go LOUD. With the $3,000 left over, I would buy the highest powered FPB series Krell you can afford or a Levinson 334 or 335 (ideally, a 336).

As for my previous post, wattage in amps is often misunderstood and leads people to buy amps that cannot do what they are purported to do. In solid-state (transistor) amps, power supply capacity is most important, which is why a very high-end 150 watt/channel amp can drive a speaker better than a typical 300 watt/channel amp. Krell will give you current, as will those Levinsons (your Proceed weighed about 1/2 of what a 334 weighs, incidentally) . I look more closely at the weight and price of an amp than the wattage rating - power supplies add weight and cost.

I would use the money left over from swapping out your Ushers to buy a Doge 6 CD player. It has a high capacitance 6-tube triode output stage with tons of punch and no lack of finesse (sells for $5k in Europe due to the import duty, but only $1,400 here).