Drew
I cant help thinking that what you want to do cannot be done.
You say you want to test 'loudspeakers'.
Firstly, loudspeaker 'characteristics ' are highly frequency dependent and a DPM is a DC instrument; so the only parameter you can measure is the voice coil resistance.
The other parameter of interest is the frequency response, and this is difficult to measure.
Loudpeakers are usually tested by 'listening tests'.
In the case of bass frequencies, the combination of box AND speaker governs the frequency response and sound pressure level with respect to audio power supplied. The speaker, box, and driving circuit impedance governs the pulse response of the system.
For more information, can I refer you to several papers on the subject.
The most modern papers of any significance are likely to be those in the name of Neville Thiele, Dr. J.E. Benson, Richard Small, but these papers are now some 40 years old.
There are probably a host of others too.
Neville Thiele particularly, was the first to analyse the loudspeaker, box, and driving impedance, to describe the bass frequency response of direct radiator loudspeaker systems.
I hope I've understood your question because anyone who wants to use a DPM as an ohmmeter to measure 'loudspeakers, cant be doing too much in the way of loudspeaker assessment.