I assume you are using the preamp stage of the Dave which is excellent.
I am a Chord dealer and am familiar with the Ultimas. They are very nice power amps but you might find the balance of that system with a Dave, Spatials and an Ultima 6 to be on the bright side. The Ultimas are more natural sounding than the old SPMs but they are still forward vs. neutral, as is the Dave. With Spatials, this could get a touch fatiguing.
Although not energy efficient, Pass would be an excellent option in terms of sound. The X30.8 will deliver all the power you need and will deliver awesome sound. I believe list on it is $6800.
Naim would be excellent with the exception of the fact that it is not fully balanced. The NAP 250 would deliver all the power you need and is really good sounding. If you are using XLRs and want a fully balanced amp, not ideal. List on it is $6900. Currently out-of-stock at the distributor but they have a B-stock unit that could be had for a nice discount.
The AVM Ovation SA 6.3 is incredible, fully balanced and everything you could want but will come in a touch over your budget as it lists at $10K. It is also way more powerful than you need but an insanely good amp. If you could trade something in, could easily be had on budget.
If you are willing to consider an integrated amp, Canor offers a 1.20 Class A SS Integrated amp that is INCREDIBLE for the money. Canor is ProJect and Musical Fidelity's Slovakian OEM. It lists for $6999.
These are all Class A or AB and will not be energy efficient. The Cass As in particular run hot at 130 degrees or so. Given how much the amp is on, would you want to consider class D? There are some newer ones that sound very good.
