I drive my VR4jrs with a Krell KRC HR pre-amp & FPB300c power amps. Sound is great, balanced tonally, 3D, airy with good bass (after loading with metallised sand - I wanted to avoid lead). I am not familiar with the 400xi but suspect that it may be less mellow than the FPB300c. One thing, you will find the VR4jr will handle much better amps than the 400xi. It really is an excellent speaker, and fantastic value.
Hope this helps.
Hope this helps.