Curious what's involved myself, found
this thread.
Makes me wonder what's involved in reverse, are transformers readily available for "normal" speakers if you have an amp capable of 70V use?
Well that post on AVS was total bunk for a start.
The answer to your question is a may be.
Is the transformer with the power taps external to the speakers?
If it is, desolder the wires leading to the speaker from the transformer.
Now take your ohm meter and measure the DC resistance of the voice coil by putting the probes on the two wires that you desoldered from the transformer. If the reading you get is between 6 to 8 ohms you can theoretically use the speakers. If not you can't.
Now there is a further problem. 70 volt systems are usually wired with high gauge small conductor high resistance bell wire. This does not work well with 8 or 4 ohm loads. So you might have to rewire.
The next problem is that 70 volt systems are mono and not stereo. So you will find the transformers will be wired in parallel, daisy chained from one speaker to the other.
So on the speaker nearest to the receiver you would have to parallel the speakers at that point, unless you rewire. You would only be able to connect to the left or right out of the receiver, not both.
Now for background systems like that there is a lot to recommend a 70 volt system.
I would seriously consider buying a 70 volt amp and driving it from a zone preout. Connect left and right zone outs in parallel.
Now when you buy the new amp, you will almost certainly have to retap the transformers. The rule is that the sum of the connected wattage taps on all the transformers must equal the wattage of the driving amplifier.
That is all there is to it. Quite straightforward really.