If these are the VTLs:
VTL S-400 Series II
They are optimized for 4-8 ohms. The Focals drop down to 3 ohms according to manufacturer specification, excluding the phase angle shift, which could be even 60 degrees. In such scenario the amplifier effectively sees a 2 ohm load at certain frequencies. If so, the amps were soft clipping those frequencies. This of course is difficult to detect with music program by simply listening because output transformers on valve amps maintain soft clipping (lower order harmonics that sound pleasant), heavily saturate the lower frequencies and limit the high frequencies. But they can't do away without the output transformers because valve output impedance is too high (low damping factor), practically impossible to drive speaker cones. Thus the valve sound (soft, smooth, warm, organic, rich, nonfatiguing).
Valve power stages are simply incapable of delivering high current for difficult loads. Keep stacking valves and you get higher power rating from the increase of voltage. Voltage is not a problem. They were invented for efficient and high impedance loudspeakers with the size of Volvo caravans.
The VTLs are certanly impressive and I would poop my audiophile diaper at such demonstration, but I think they tortured them with those nasty modern Focals. If I would get pure valve amplification, the speakers must be technology matching the same era the amp was designed in.