I have a Winsome Labs stereo amplifier which has a full bridge output. The speaker negative terminals are not at ground potential but are actively driven. As such they can not be shorted together.

Some subwoofers internally short the speaker-level left and right minus inputs together. Can anyone advise whether the EP125 does so, or are the left and right speaker inputs isolated from each other and thus safe to use with my amplifier?

You might have to contact Axiom directly for this one... either the "advice@..." email or phone.

Are you thinking about replacing the EP125's internal amp with this amplifier?

I am betting he wants to bridge(this is that term I couldn't think of but thankfully Eric did, during Mojo's 260W 3808 episode) it, to give it more power.

No. I want to connect the subwoofer (using its internal amp) to the system using the speaker-level subwoofer inputs (binding posts). The negative speaker terminals on my amplifier are not at ground potential as the amplifier has a balanced differential output stage.

Thus I need to ensure that the subwoofer doesn't internally connect the left (-) and right (-) speaker-level input posts to each other. I could do this with an ohmmeter but want to verify that it is OK before buying the subwoofer.

Whether or not speaker terminals are at "ground potential" (I ma not even sure where that is coming from actually), you can NEVER make speaker connectors touch as this is call a "short" and is usually followed by a huge series of clicks as your receiver goes into protective mode. So either your question needs to be formulated differently or you have nothing to worry about as these sub-woofers and something a million Ohms of resistance on those speaker terminals.

Why not just split the preamp signal and send it to the sub and then to the amp? Problem solved.

I see what you're saying. Call Axiom--no one here is going to know.

The volume control is part of the amp, so every time I change volume I would need to change the level on the subwoofer.

Do you not have a preout on this amp?