Please take into account that if one uses tubes specifically not recommended by the manufacturer, you are doing so at your own risk. I own REF 250 (not SE) amps and spoke with my dealer and with Audio Research representatives at the company about using KT150 tubes and they told me that several expensive upgrades must be done to properly allow for this use.
Expensive transformer life may be shortened. I'm good with the KT120s.
If, I decide to upgrade the amps to REF 250SE amps, then Audio Research will perform the upgrade, which includes the addition of KT150 tubes.
I've already spend a few thousand on repairs of one of my amps, simply because one of the tubes blew spectacularly. It took out some caps and resistors and an integrated circuit also. I was trying to save money and purchased "matched" tubes from a well known tube supplier.
The authorized Audio Research repair facility told me that they never uses tubes from that supplier as they aren't spec'd to Audio Research standards.
Anyway, unless you are prepared to come out of pocket for expensive repairs down the road, I wouldn't use tubes that the company doesn't approve of.
enjoy