Could you define " really low impedance"...Loudspeaker impedance varies with frequency. A loudspeaker with an "8 ohm" rating can dip as low as 4 ohms at certain frequencies. Certain speakers drop to 1 ohm ( Martin Logan ).
I have never owned a pair of Saras', but looking at a few google images, the tweeter looks like a scanspeak d2008 ( shouldn't give ANY impedance problems here ), the woofers are KEF SP1004 8" units in parallell. ( true isobaric ) wiring. You will get some dips into the 2-3 ohm range, but unless you are driving test tones through them, I wouldn't be too concerned.
If you want to see the worlds most USELESS owners manual, go here : http://www.linn.co.uk/owners_manuals
and look up the SARA manual.
I'm quite familiar with many carver products, but not so with a 6250. Anyone else care to wade in ?
Rob