Is there a cable maven in the house?

There are cables that will connect an unbal/RCA source to a bal/XLR input but there is not guarantee that they will work well in all situations. Cardas makes some as does Hosa.

OTOH, there are adapter boxes for this and these are much more likely to work fine with an RCA cable on one side and an XLR on the other.

The Jensen is excellent http://cgi.ebay.com/Jensen-Transformers-PC-2XR-XLR-RCA-Audio-Converter-/360356008112 but there are cheaper: http://www.google.com/products/catalog?hl=en&safe=off&client=firefox-a&hs=441&rls=org.mozilla:en-US:official&q=rca+to+xlr+converter&revid=1610109775&bav=on.2,or.r_gc.r_pw.&biw=1680&bih=869&um=1&ie=UTF-8&tbm=shop&cid=17143747499655455269&sa=X&ei=FhsJTsLIBMf20gHT0qCOAQ&ved=0CEkQ8gIwAQ

Just get the Jensens which have high quality transformers in them and which sound excellent by doing nothing wrong.

The PC unit listed above converts "Pro" +4dBu signals to "Consumer" -10dBV signals. I am not sure that is what you would want. I suspect the input transformers "PI" would better meet your needs, such as the PI-1RX meaning one channel per box (because your speakers are separated you will need two boxes) and also that it changes RCA signals to XLR. You should run very short XLR cables from the boxes to the speakers (no more than 1M). The best way to find out for sure what you need is to call the helpful folks at Jensen. Here is a link;
http://www.jensen-transformers.com/iso_aud.html

I have used both the BAT and Cardas adapters successfully. BAT are more robust -- but more expensive. Cheaper adaptors from other suppliers break easily.

Neal

Lindisfarne 06-27-11:
What is the best way to accomplish the connection?

The best way is with a suitably chosen Jensen transformer, as indicated above.

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

There are ways described above will work, but to have a true balanced chain I'd replace preamp(which I did myself a while ago). The ideal case when you have directly coupled balanced (no transformer no capacitor) connection between components to have minimum noise and maximum transparency.
Among the choices above I'd choose Jensen transformers that would actually convert your signal to balanced.

Thanx all. You folks are great (and helpful). I spoke with Jensen today.