Best replacements for KT99A tubes?

I have a pair of Cary monoblocks with two broken KT99A tubes. As they are impossible to find, my plan is to replace them with a full set of new-manufacture tubes. I was looking at 6550's, but not set on anything yet. From reading various forums, I've identified the Gold Lions, Tung Sul, and Svetlana, but I haven't read anything that makes or breaks the decision for me. I'm looking for any and all input or suggestions! This is all very new to me, and I want to get something that will do justice to these very nice amps.
KT90 maybe but a 6550 is not a proper, appropriate, suitable substitute for KT99A in any amplifier intended for installation, use, or operation in a Music Reproduction System.

Is this for the SLM-100 or SLAM-100 monos by chance?

If so, shows in the OM they originally came with 6550s. Original OM mentions max bias adjustment of 175ma for all four tubes per amp, with potential use of EL34, KT88, KT99s. Maybe go 160ma to start, 40ma per tube. Lots of old references, some using JJ KT88 Blue Glass back then.  And, I recall seeing several running them with Gold Lyon Gelenex KT88 reissue too, fwiw. Recommends matched quad (of the same type tube) per amp if you replace them.
@clearthink Damn! Could you be any more clear? :P Thank's for the input. Can you elaborate on *why* you have such strong feelings? I haven't seen anyone as decisive as you be anti-6550.

@decooney This is for a pair of SLM-100's. You remind me I need to track down an original owners manual... I'm definitely planning to get matched quads. Any thoughts on EL34 vs. KT88? I had the sense that KT88's were higher quality somehow to the EL34.