@OP. Put simply, take the manufacturer's nominal impedance for the loudspeaker and, on a precautionary principle basis, assume that it is optimistic - because they frequently are. Check the specifications for efficiency as well and also assume that they are optimistic, but most speakers are around 87dB unless they are minimonitors or specifically designed to be driven by low powered, mostly tube, amps. Check the amp manufacturer's specifications and check out reviews as well - look for amplifiers that will double their power from an eight ohm to four ohm load - if they are solid state amplifiers. That approach should avoid the most obvious mismatches. After that its a question of budget, where you sit in the room and how much bandwidth, volume and dynamics you want. Maybe there will be more choice/listening opportunities in the area you are planning to build the second house?
Determining compatibility with amps
I have a pairing that has been wonderful to me and I may also be looking to set up another similar price-point system (streaming only, larger room) in another house we may build as snow-birds. While very happy now, I want to know more about how to pick speaker and amp pairs to make them more compatible and not ill-advised. No, I don't get to audition equipment (I live in Alaska). There is not a club here. Heck, there's only BestBuy with a Magnolia room. Just "let your ears be your guide" isn't a big help. Help me understand how I can narrow the search for "kinds" of speakers and topologies of amps for my possible upcoming build. I have gathered that using speaker plots, it's the areas where the phase drops below zero (capacitive), coinciding with low impedance that are to to be avoided. I've looked at several sets and can see for example, why series XOs might be desirable. I guess I'm asking is, what values/relationships constitute "be careful" or "avoid"? And if there technically are real issues, what are the audible affects, or kinds of audible distortions one might expect? While I'm not married to tube amps, switching to this one was a very large improvement. I love the voicing/timbre, imaging, and they definitely disappear. It's almost scary.
I'll ask to avoid making pairing suggestions but instead try to help me understand, "these (kinds) are good for this kind of amp because"... My virtual system is up and I've included my speakers' plots as an example by which to comment or use as an example. I welcome using them as a discussion point. FWIW, my amp has an 80hz hi-pass that I use. One reason I like it, as mid-sized stand mounts seem to be what I lean towards, is this aids with integrating subs. Maybe the best answer is to duplicate it all! I may be traveling soon so I may not post often but will read everything for sure! I've got a technical background (the reason I ask) but not in EE so be gently. Curious minds just want to know.