90db 4 ohm with tubes?

I have the Dyn C1's (85db @ 4 ohm) and have driven them with an Octave V40se - V70se and V110. No problems at all.

I would say in general tube amplifiers respond favorably to higher load
impedance and potentially sound their best under these conditions.
However if the tube amplifier has good quality transformers, stiff power
supply and 4 ohm taps they can work well with 4 ohm speakers.

I heard the 4 ohm 89db Dynaudio Evidence Platinum driven by the Octave
push pull amplifier and the sound was just excellent.
I've heard the 4 ohm 91db Rockport Altair driven by the VAC Phi 300.1 (PP)
amps and also driven by the Absolare Passion PSET amp and these
produced much better sound than the MSB solid state amp on this fabulous
speaker.If your Cary amp has high caliber transformers and power supply
you'll be fine.

Regards,

Your amp should have no problem driving those speakers. Not only that, you can probably get good results running you amp in triode mode. If you have a good local dealer, they will almost certainly let you bring your amp into the store and try it first.

Assuming you are referring to the current Diamond DMD version, the impedance curve shown in the review Samhar referred to indicates an impedance rise to around 28 ohms in the upper mid-range, some smaller impedance peaks in the deep bass region, and, according to the text of the review, 4 ohm impedance minima with "overall measured impedance [of] 6.5 ohms, so this is nominally a 6 ohm loudspeaker."

The rise to around 28 ohms in the upper mid-range will result with your amplifier in somewhat greater emphasis of those frequencies than would occur with nearly all solid state amplifiers, and also with some tube amplifiers (those having lower output impedance than I believe yours does). There will also be a bit more emphasis of frequencies in the vicinity of the two impedance peaks in the bass region.

I don't know whether or not with those particular speakers and your particular amplifier that would be good, bad, or something that comes down to a matter of taste and room-matching. But it's something to be aware of.

Regards,
-- Al

looks like the sound will sacrifice tonal balance.
upper mids emphisis will create fatigue.