I thought it shouldn't be a difficult decision because if you need more power, it will be the RB1590. In that case, it would be better to pair it with the RC1572, not the RA1572. If it is not about power, then you can just choose the one that looks better to you, for me it would be the AS-2200 and I like the fact that it is a plan integrated amp, without the DAC, that I would much prefer to choose my own instead of forced to pay the one I may not prefer.
Other than that, I see that neither has SOTA specs but both should have distortions low enough to be below the threshold of audibility. I am bias, if I were to spend $4,000 to $6,000, I would go with something that have SOTA specs and measurements, probably something like the AHB2+ a preamp that has the specs to match, and a separate DAC. DACs that are built in (such as the Rotel's) are typically, or never picked from the flagship models of the major brands such as AKM, ESS Sabre, TI, Cirrus Logic etc., so I doubt that Rotel would be any exception.
