hmmm, i'd go for the RA-06, there is most likely to be a difference between the 2, being that the ra-06 might be able to give you more bass (more loudness in fact), it will also play a little cleaner, there is somekind of a rule (not really a rule, more a guideline), the more watts, the better, this, of course, does not apply for those cheap crappy party 'power' amps.
anyways, i'd go for the RA-06, if you can, you should audition the ra-05 too, and whichever one you buy, they both have pre outs so you can add an extra amp (power amp) when you feel like you need more power.

Greetings,
Basite.