If the Dalis have as flat an impedance curve as suggested (as the Megalines do) that will help with the use of a tube amp.
None of our customers have reported any feedback (we have excellent feedback on the Megalines) so I am only going by the numbers on their website. 86 db is pretty inefficient, but if they are being conservative and stating their numbers (89 db, 2.83V/1 meter + 4 ohm impedance= 86db 1 watt/1 meter) from the bottom of their curve, the speaker may be easier to drive than their website suggests. A lot of course depends on the room and listening habits!