Stereophile has a full set of measurements on the Blade 2 and it primarily shows the speaker requiring full 4 ohm stability with an ability to be fully stable to a 3.2 ohm load. This will simply require an amplifier with adequate current capability. As an example, some of the older ASP1000 based amps did poorly with lower lower impedance speakers than their ASP500 counterparts on some speaker models. The reason was due to the first generation higher power amplifier apparently being less comfortable in dropping below 4 ohm than its lower specified counterpart.
In terms of the Rowland, it does specify near doubling of output at half impedance with the 725 mono blocks as compared to the 625. Most of this load is below 200hz and rises to 6 ohm nominal above it. This could explain the spotlighting phenomenon since we know the B2 goes as low as 3.2 ohm in this area. My suggestion is to try and mate amplifiers that offer 2 ohm stable output in order to prevent the amplifier going anywhere near its potential current reserve. One suggestion would be some of the Pass Labs models, as some are capable of power into 2 ohm loads without much stress. This factor is tough to know until you get the amp on the bench. Even then, there is something to be said about overall synergy.
In terms of the Rowland, it does specify near doubling of output at half impedance with the 725 mono blocks as compared to the 625. Most of this load is below 200hz and rises to 6 ohm nominal above it. This could explain the spotlighting phenomenon since we know the B2 goes as low as 3.2 ohm in this area. My suggestion is to try and mate amplifiers that offer 2 ohm stable output in order to prevent the amplifier going anywhere near its potential current reserve. One suggestion would be some of the Pass Labs models, as some are capable of power into 2 ohm loads without much stress. This factor is tough to know until you get the amp on the bench. Even then, there is something to be said about overall synergy.