You are only going to be able to listen so loud before your ears bleed, you go deaf, and the rest is just Headroom.
I emailed a few times with a VP of Regional Distribution for MA (their North American importer)... His message to me re: the Silver 500s was that I could use a 1000 watt amp, the speakers would sound great... and then I learned I would never actually use that much power.
Ever.
In short, headroom isn't a bad thing. Don't be afraid to have enough juice available to push the speakers to, or just past, reference level peaks.
Those Bronze 6s are rated at 90dB, so depending on your room size and distance from, 128w gives you 111dB @ 1m... assuming a large room without benefit of reinforcement (thus a 6dB loss in SPL), you will be at 105dB peak sitting about 6-7 feet away.
For intermittent, real world power usage, those speakers can handle more. If you want to stress test them and run 150w sine wave through them for an hour... you might blow them. (Or if you want to run them Large with a 16hz Pedal Tone from a large organ and you turn the volume up to 0 or +5... you could expect to damage something.)
But short of that, you could buy a 300w RMS per channel amp and you would be fine (as long as you don't abuse it). My 2 cents... YMMV