First, the Q7 are much easier to drive than the Q5. Yes, they are a 4 Ohm speaker and 94dB is rated at a 8 Ohm standard. So you can adjust down sensitivity to 91dB. Even at 91dB, they can still be considered as high efficiency speakers, even if far away from what you can achieve on horns...
The Spectral DM260 had no problem at all driving it in a big room at a dealer demo during Munich show, so I wouldn't say they need "big power" to work well. But the load is still not an easy one, so you need an amp with good current capability.
The small Dartzeel may be able to drive them, but of course it depends on your room side and how loud you are listening. What a bigger amp brings you is headroom, and very high peak power: the power supply is big enough that you never get current limited. The Q7 are the most dynamic speaker I have heard: you will benefit from extra headroom, because unlike most speakers on the market, the limiting factor will be the amp, not the speaker itself. That's why I believe they would sound much better on the big Dartzeel: it has a refined sound with very nice decay of notes and it is at the same time extremely dynamic, with explosive power.
More important than big power, you need clean and "fast" power. These speakers are so transparent that you hear absolutely everything you will feed them with. So they deserve being fed by the best. At the end, if I would have to chose between feeding them with 250W of extremely refined and transparent power and 600W of an amp a bit less transparent, I would go for the first...