I run amps older than the DNA1s and have zero issues with them. If you're hearing popping and clicking noises I doubt it's from your amp.
One thing that hasn't been mentioned here related to your cabinet situation is ventilation. If it's as tight as you say, I'd be worried about cooling with many amps (and I think the DNA needs ventilation).
Another option is a new class D or hybrid amp. I have a PS Audio HCA-2 that sounds great. They can be found used in the $600 +/- range. They are recent production and run very cool, and consume little energy at idle. The also aren't terribly big.
One thing that hasn't been mentioned here related to your cabinet situation is ventilation. If it's as tight as you say, I'd be worried about cooling with many amps (and I think the DNA needs ventilation).
Another option is a new class D or hybrid amp. I have a PS Audio HCA-2 that sounds great. They can be found used in the $600 +/- range. They are recent production and run very cool, and consume little energy at idle. The also aren't terribly big.