This is an interesting topic (to me).
First: I like Carvin and am happy with all my Carvin purchases, and especially the attentive service.
When I ordered my BX515 they told me that it was 4-ohm (to get all the power n the combo), since it didn't really matter to me at the time, I said OK.
I treated it as a 4-ohm and everything was OK until I blew it up, I think that I had a speaker wire short, and it went into protect mode and wouldn't come out. Carvin replaced the head with absolutelly no hesitation.
While the heads were being exchanged, I removed the speaker to look at it, and it was very clearly an 8-ohm model, per the label. I then posted a question in this thread about how to determine the ohms for a cabinet. I checked it out and the cabinet came in consistent with and 8-ohm cabinet.
I called Carvin to try and reconcile what I had been told with the facts as I saw them. The sales guy insisted it was 4-ohms and the tech guy said it was definitely 8-ohm. In any case, I'd make sure that you get what you want when it's delivered.
Another note. They advertise the BX515 as weighing 40 lbs. It's actually 52 lbs., but still light by my assessment.
FWIW