Trich, in view of the very high probability that the MC2700 has a different input sensitivity than the Threshold amp, you will probably be creating a level-matching problem if you go that route. You would likely have to address this issue with any tube amp you would use on the top as well. It could be dealt with by inserting a passive preamp in line with the amp with the higher input sensitivity and then turning down the volume slightly to match the level of the less sensitive amp. Of course if you used another amp with the same input sensitivity as the Threshold there should be no need for the level matching.
My guess is that if your Threshold is "silk-smooth," you would derive little or no benefit from adding a solid-state McIntosh unit.
My guess is that if your Threshold is "silk-smooth," you would derive little or no benefit from adding a solid-state McIntosh unit.