Analogbox....I have been following your journey with the K1000 and thought I would offer a few suggestions.
I saw a suggestion earlier in the thread regarding running your Aleph without a preamp. NOT A GOOD IDEA as the Alephs have low voltage gain and as such do VERY poorly running direct from a source, and passive preamps as well. Keep your Decware in the setup.
Tubes.....
The Sylvanias are decent 6922s ...BUT they do have a brighter tonality and also lack refinement in comparison to many others. I would look for some Matsu****as. These are 6922 tubes that can still be found for sane prices in comparison to the Mullards. These were made in Japan and with Mullard tooling. They sound VERY similar and internal construction appears the same.
They are smooth,refined and slightly warm sounding and have great inner detail that sucks you into the music.
Cables.....
I have experimented alot here, trying many DIY designs including VH recipe silver cables, cables built from stranded copper and many others. In the end I ended up using one of my old trusty favorites ,that being cables built Tara Labs. I have been fond of their cables since the late 80s. Their cables are of solid core copper construction and work wonderfully with the K1000s. They offer everything one needs in a K1000 rig including some warmth without any loss of detail. Refinement, spaciousness and solid 3D images is a strong point of their cables in general. (some of their older stuff can be found on Ebay for decent prices)
Sources.....
Pretty obvious here as bright, hard and or overly "digital" sounding sources need not apply.
Other Stuff.....
Don't overlook the simple task of positioning the phones themselves. Getting the right driver toe out and front to back positioning on your head can have a substantial effect. And different positioning may be desirable for different recordings.
Also keep that Aleph plugged directly into the wall outlet and NOT through any power conditioner(s). It will really suck the life out of the setup.
All of this is IMHO and nothing more. I hope some of it helps.