Hi Dan,
I don't see any problem there. Martin Colloms' measurements in the review I linked to indicate that the power amp's input impedance is 50K (although the quoted specs say 100K!). So the two channels in parallel will present to the preamp a combined load of 25K. That won't result in a significant reduction in sensitivity (or significant frequency response unevenness, either) with nearly all preamps, especially solid state ones such as Toby's MC-7, since the preamp's output impedance will be vastly lower.
The lack of separate buffering on the two output jacks also means that the two-cable approach Toby was considering would result in the preamp's output stage seeing nearly twice the amount of cable capacitance as with the y-adapter approach. That could result in perceptible upper treble rolloff if cable lengths are long, the cables do not have low capacitance per unit length, AND preamp output impedance is high. But again, in this case the output impedance of the preamp is most likely low enough for that to be a non-issue, regardless of which approach is chosen.
Best regards,
-- Al