Fullest potential is not going to be pair of Vidar's. TBH, I don't know where that point is for the SR1a's. I know that I like the way Spectral interacts with the SR1a's, and I know what Spectral pieces will actually fit inside my room. But I could dump another $30k into that stack and it will just keep getting better, and I know this from swapping out preamps and power amps all the way up to their flagship monoblocks driven off a 30SV. As Srajan at 6moons put it, you want to drive them as if they're $10k+ bookshelf speakers, not as a pair of $3.5k headphones. The real question is what part of the performance frontier do you want to maximize (speed? midrange? control? resolution?) and how much you're willing to spend toward achieving that. You might lose more money trying to sell two Vidar's compared to, say, selling a used amp or even a demo unit from a local 2 channel store. Some of the best power amp deals I've ever found were from local dealers looking to bring in new gear and liquidate older gen products.
There's nothing wrong with the SR1a on cheap equipment, at least to my ears. But if you really want to achieve a point where bass quality and midrange performance isn't being held back by the amp, I think starting at $2k - 3k, preferably used, isn't a bad idea.