@avanti1960 Thanks for your comments about the benefits of a preamp or integrated. The RME UCX II provides preamp functionality, including volume control, multiple source selection (both analog and digital) - and selectable gain levels. Consequently, to get the tube sound I thought I had to focus on a tube power amp. However, if most of the tube effect comes from a tube preamp section then an integrated amp, possibly hybrid, might be my best bet.
At the risk of displaying my ignorance, the UCX manual states that audio line out gain is selectable at +19dBu, +13dBu and +4dBu. I don’t know if that would help with my 87dB Stirlings.
@pindac I, too, am a fan of the newer class D amps. But I just didn’t think I could get sound I’m after without going the tube route. Maybe I’m wrong. Presence, envelopment, warmth along with precision.
@elliottbnewcombjr Maybe part of my problem is that my LS3/6 are undersized for my room, as you seem to be saying- or that the combination of my room size with desired tube amplification does not work well with 87dB speakers. Ugh.
Anyway, these comments are very helpful. Thanks.

