Dentdog, I don't see any issues with what you've described. In fact the design of the Leto seems ideally suited to a situation involving a lengthy connection to an unbalanced input.
John Atkinson's measurements of the output impedances of the Leto were even lower than specified, and as I'd expect in the case of transformer coupled outputs did not have much variation as a function of frequency. That will make the capacitance of the long interconnects a non-issue for any reasonably designed cable.
Also, I don't know if you are using RCA cables or XLR cables + adapters to mate with the unbalanced inputs of your MC60s, but either way you are in effect running unbalanced interconnections since the load is unbalanced. However given the transformer coupling and the provision of ground lift switches in the Leto for its unbalanced outputs you presumably are immunized from ground loop effects that can occur in some cases involving long unbalanced interconnections.
Also, actively driven balanced outputs on some equipment (as opposed to transformer coupled outputs) may have problems with XLR-to-RCA adapters, since most such adapters short the signal on XLR pin 3 to ground (XLR pin 1). But again that won't be a problem with a transformer coupled output, and in some cases involving transformer coupled outputs it may actually be necessary for an adapter to connect those pins together.
Enjoy! Regards,
-- Al
