I have Vox AC4 amplifier which lack of FX loop.

Hence, it is possible to add the effects only in front of the amplifier. The chain would be: Guitar --> looper --> Reverb --> Amp

Because the looper is in front, there is an importance of matching of the impedance for the rest pedals:

from looper I will have 330Ω of the output

HolyGrain which is stomp box has 680L Ω on intput and 360Ω on the output RV 300 which is modulatory pedal has 250KΩ on input and 1K Ω on output

What is the better option assuming that I would like to send to Ac4 a very undisturbed in terms of frequencies range signal and ii) not lose the amplitude of the signal because AC4 lack of the head-room ?

Thanks you!

Gleb