I've just found your post. I use a SW 900 and still have the manual. Here is what it says in the Specifications section:
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Type: Super Woofer system with built-in anti-magnetism (EIAJ) amplifier.
[Amplifier]
Practical maximum output: 70 W (50 Hz, EIAJ 10%, 6 ohm)
Frequency response: 20 Hz to 60 Hz, 90 Hz, 120 Hz
Phase switching: NORMAL, REVERSE
Input sensitivity & input impedance:
RCA-type pin-plug jack: 100 mV / 70 W 6 ohm, 5k ohm
Push-type terminals: 1 V / 70 W 6 ohm, 12k ohm
Supply voltage: AC 110 - 120 V~, AC 220 V~, AV 240 V~
Rated power comsumption: 80 W
[Speaker]
Enclosure: Front-load, bookshelf type
Speaker units: 160 mm (6.5 in) cone type x 2
Nominal impedance: 6 ohm
Dimensions: W 210 mm, H 559 mm, D 412 mm
Net weight: 13.5 kg
Supplied accessories: Pin-plug cord 3 m x 1, Remote control unit x 1,
Battery (SUM-3) x 2, Adapter x 1, AC plug adapter x 1
* The "anti-magnetism (EIAJ)" term refers to a speaker system designed in compliance with the technical standards of EIAJ (Electronic Industries Association of Japan).
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I think what is important to you is that the two speakers are both 160 mm cone type 6 ohm capable of handling 70 W between them.
Hope that helps.