help vandersteen quatro & bat amps

When configured as mono-block, its input impedance is cut in half.

originally impedence of vk55 stereo is 215K so monoblock is 107K??

accordingly, how shld the high pass filter of the quatro be configured?

Nt comments?

Yes. That is correct. You can set the high pass filter at 100K. You can also try
75K and 150K setting and see which one sounds best. Impedance on a spec
sheet is typical value which may not be the value at 100Hz.

If you want to be precise, you will need a multimeter, a dummy load, and a test
CD with 100Hz and 1000Hz signals; and pick the closest setting which gives
3db lower output at 100Hz than at 1000Hz.