What to pair with stacked Large Advents

The advents are on the A channel in series. The B channel is open.

Since you have Advents, the Baby Advent should be a good match.

Not a bad idea. Never heard them but probably a good compliment to the large ones. Thanks!

Refurbished Small Advents would be a much closer tonal match (than the Baby), plus they will perform better @ higher SPL's.

Owned stacked Large Advents in the mid 70's and when ran as single pairs preferred the Small Advent (over a pair of the Large).

Never tried stacked Small's (wonder how they would sound).

I personally wouldn't add a pair of 'rear' speakers. I don't think the Luxamn could handle it, it would take away from the power needed to push the stacks. I had fun refurbishing two pairs of Advents myself, the stacked pairs can sound almost concert level.