There’s nothing wrong with your speakers. I’ve heard the R900 with a 30W tube amp and it was a very pleasant listening experience. The R series is the entry-level for KEF, so there is some cost cutting to the cabinets and bracing, but not the drivers and crossovers. These speakers are revealing, dynamic and throw a huge soundstage.
Although listed as an 8 ohm speaker, the impedance curve indicates a large part of the all-important low and mid-bass frequencies are at about 4 ohms. So the 4 ohm taps should be tried first, as stated in the above comments.
Although listed as an 8 ohm speaker, the impedance curve indicates a large part of the all-important low and mid-bass frequencies are at about 4 ohms. So the 4 ohm taps should be tried first, as stated in the above comments.