I'm afraid that I have a mostly contrarian opinion that falls in-line with Timlub's thinking on vintage vs. modern speakers. I don't think that modern speakers are necessarily better SONICALLY than their vintage brethren. Yes, BUILD-wise, the modern speaker has a lot of positive attributes going for it such as better manuf technologies & more tightly controlled manuf process for speaker drivers. Yet, given these 2 items, it does not mean that the speaker manuf will do a better job designing a better speaker today vs 30-40 years ago. In fact, quite the opposite! My experience from audio shows, listening to people's systems in the USA & over-seas tells me that most modern speakers are SONICALLY no better off than the vintage equivalents.
Modern speaker tout modern materials such as Kevlar, aluminum, Berrylium, etc, etc but I have yet to come across very few select speakers designers who can use these modern materials to their advantage to make a speaker that sounds like real music. 99% or more of the modern speakers just cover up their dismal performance but touting exotic materials, CNC machining, CAD design of their x-overs, etc, etc. When you have a 1-1 conversation with the speaker designer, I quickly realize that they have very little in-depth knowledge of the effects of their x-over & what it does to the phase of the music signal. Many don't even realize that preserving the phase of the music signal is the name of the game in speaker design. Many others do but they don't know how to solve the problem so they cobble together some highly compromised solution that is good enough knowing that the consumer's eyes will glaze over when the throw out some buzz words if they (manuf) are questioned by the consumer.
Further almost all modern speakers have impedance & phase curves are worse than the most hellacious roller-coaster you have ridden. These fast changing one-moment capacitative-next-moment-inductive impedance/phase plots will drive almost all amplifiers to their knees leading to only sonic dissatisfaction. Only the hardiest (& obviously very expensive) amplifiers will be able to muscle the modern speaker into producing reasonable sounding music. Most other amps will output sound from the speakers but they will leave a lot to be desired. The user will forever be on the audio merry-go-round. In fact, there is even a thread to this effect on the "tech" or "misc" forum.....
I realize that the OP has cited his SAE amp's specs & even informed us that Pass or a close associate of Pass had a hand in designing this amp. Having a famous person design an amp means only so much w.r.t. its sonic performance. The amp-speaker interface is very important (discussed at quite a bit of length in either the Amp or Speaker forum. Might be worthwhile reading that thread to narrow down which speaker type will fit best with your SAE amp) & most people put very little thought into it only to be disappointed later on. A solid-state amp's current delivery into a varying load, dynamic headroom, (for me) bipolar vs MOSFET, negative feedback, signal bandwidth, power bandwidth, output impedance are some of the criteria that set one amp apart from another to do the right job for the speaker in mind. If you are going to fix the amp (SAE) better ensure that the speaker selected can electrically mate with this amp.
Purchasing a modern speaker by no means implies sonic pleasure when installed in one's system. Just troll the Speaker archives on Audiogon & on AudioAsylum if you are not convinced. Very few modern speakers will give you long-term sonic pleasure & almost all of them will cost you more than $1500.
Many vintage speakers in good condition will last for a very long time - several have cited Infinity & AR as some of those brands. There are several planar speakers too that fit into the excellent-sounding, good-condition vintage speaker category. Yet another brand with superb sounding speaker is Tannoy - not mentioned before - esp. those that used their 15" Alnico magnet dual-concentric drivers. I believe one can DIY one's cabinet & also buy ready-made cabinets if one can get hold of these Alnico drivers. And, many vintage speakers will sound just as good if not better than modern day speakers with just a component upgrade to their x-over. Infact, I'll 2nd Larryi's post in saying that some of the best sonics I have heard are from speakers using 1920-1950s speaker drivers in modern manuf cabinets.
So, don't rule out vintage speakers from your search list. In the end, none might fit your budget/space/looks criteria, so be it....
Just my 2 cents worth, FWIW. YMMV.
