Bi-amp befuddlement

Newbie in midst of modest upgrades to old system and wondering if I am getting best benefit from bi-amping:

Having read about it, I acquired an Arcam 8 power amp to pair with my Arcam 8 Integrated.

Speakers are B&W 601 S2, about 20 years old, which sounded quite warm and nice bi-wired with Monster cables. For the bi-amping effort, I bought Anti-cables.

I followed the Arcam instructions and wired the power amp to low end, the integrated to high end. Frankly, not sure I noticed a difference - except maybe when I crank it up. The sounds seems clearer, with less distortion, or maybe that's wishful hearing.

I am questioning things in part because the other day, I shut down the power amp and the music nstantly went tinny, like some tranmission from space. Put on the power amp, and all richness floods back. Clearly, I expect a change but not such a massive one.

Is that normal? Is that all I am getting out of the intergrated? I have looked at Audiogon forums and read about vertical bi-amping - one amp per speaker. Is that a better use of two amps for somebody who is not going to mess with speaker cross-overs?