Balanced vs RCA preamps

The quality and sonic characteristics of the preamp are of the highest importance and the interconnect capabilities are of a vastly smaller or of no importance. But the world is slowly migrating to balanced. On some equipment they may sound slightly better.

For instance, I compared balanced and unbalanced on my current Audio Research equipment and I couldn’t tell the difference. Audio Research recommends balanced, but does a great job of converting to non-balanced.

If all else is equal... and it virtually never is... you want the option for either. There is a slow migration from unbalanced to balanced. You can save money by using unbalanced since often quality interconnects are much cheaper.

If I could get an older high end Conrad Johnson preamp for instance, that did not have balanced over a much lessor preamp with balanced. I would do it. 

The short answer to your question is, it is not a good idea to base your decision on which preamp to buy solely on the basis of balanced outputs.  First of all, they do not exist for tube equipment, maybe there is a hybrid out there I am not aware of, but for all practical purposes anything with XLR connections is going to be solid state.  Nothing wrong with that, if that is what you want of course.  Next let me share a recent experience with you, admittedly this is only anecdotal, but I think it helps to frame this discussion.  In my main system, my line stage is a Conrad Johnson ART Phono, this is that company's current top unit, and retails for $28K.  It is pretty good.  It has only RCA of course, because it is a tube preamp. For my second home I recently put together a new system.  For it I purchased an integrated Marantz PM10 and it has XLR connections. I also have on hand a Precision line stage, a $50K unit. While I had these all together one of the things I did was compare XLR and RCA connectors.  Without getting into great detail, I learned that both the C-J and the Precision line stages sounded better than than the Marantz PM10 the one integrated into the unit even when using RCA connectors (Audio Sensibility Statement Silver).  That should surprise no one.   I also learned that RCA connectors as above sounded better than a Shunyata XLR connector (Gamma) when used to connect either of two cd players (Luxman D-10X or Marantz SA10).  So, from that I conclude that there is more to the matter than merely what kind of connectors are used.  Therefore, that is not a good criterion for basing a decision on what component to buy.  It might be a tie breaker if all else was equal, because when I compared two equal connectors one RCA and the other XLR there was a small difference in favor of the latter.  Let me be clear, though, with emphasis on the fact the the difference was small. 

I use Ayre equipment.....all the components even the phono are balanced

Ayre is all solid state, no tubes.  The OP wants balanced and rca on a tube preamp. 

My Linear Tube Audio MicroZOTL tube preamp has one balanced input. The rest are unbalanced.  I asked LTA if there was any benefit to using the balanced input. They said it would depend on the strengths of the connected device. My dac has both balanced and unbalanced outputs. 

I'm using unbalanced because my best cables are unbalanced.