Then you'll be able to run 6CG7's as well. Also 6BQ7/6BK7 but those have mu of ~40 instead of the 5687's 16.I have a sack of 6H6Pi tubes. GOt those wonderful things for $2.45 each. They are a nice alternative to the 5687.
I can't say I've ever found the 5687 hard, save at very low current like 2 mA or so. Usually I find it a bit to soft...heh-heh-heh, audio language and at best small computer sound systems to sort it out.
I am sort of stuck on the 12B4, and wish I could have one like it with about mu=3.
cheers,
Douglas