Lindisfarne 06-27-11:The best way is with a suitably chosen Jensen transformer, as indicated above.
What is the best way to accomplish the connection?
With respect to the lower cost approaches, using an adapter or an adapter cable will function. However, an important question is whether or not the amplifier in the speaker is "fully balanced," or if it converts the balanced input to an unbalanced signal which is then put through an unbalanced internal signal path.
If the amp is fully balanced, you would not be able to utilize 3/4 of its power capability (i.e., a 6db reduction in maximum power) using an adapter or adapter cable approach, because no signal would be going through one of the two balanced signal paths. You would also be negating many of the sonic advantages of fully balanced design.
If that is not the case, and you want to consider an adapter or adapter cable approach, a properly designed adapter cable is preferable to a male rca-to-male xlr adapter + xlr cable, because fewer connectors are involved, and both of those approaches are preferable to an rca cable + female rca-to-male xlr adapter, which will not provide the noise and hum rejection performance of the other two configurations.
The configuration of a properly designed adapter cable is shown in Figure 2.1 of this Jensen white paper. Note that two-conductor twisted pair shielded cable is used, with xlr pin 1 and the rca ground sleeve connected to the shield, and with the rca ground sleeve also connected to one of the two conductors, which is connected to the inverting or "cold" xlr input pin (usually pin 3) at the other end. The rca center pin is, of course, connected through the other conductor to the non-inverting or "hot" xlr input pin (usually pin 2).
Regards,
-- Al