Arcam HT amp? Do you mean Arcam receiver or Separates?
If the former, you sould consider sticking with higher sensitivity and efficiency designs, to keep dynamics up! I certainly wouldn't look at 85-86 db designs with a receiver, even though you WILL run them as "small" or 60-80hz cutt-off, which will help.
That said, I'd look at simple crossover or crossover-less designs, maybe horn or Dappolito configured speakers, speakers with active woofers, and other more efficient ht speaker offerings. Alot depends on acoutics and room setup however.