Tube upgrade for VAC Ren 30/30

Hi all,
Now that I can finally start dabbling a bit in in higher end analog audio, I had a few questions to ask of the community. First up is one regarding tube upgrades. I'm quite new to world of tube-based amplification, and after much research and auditioning I'm just finishing up building out a system that I think will work for my needs.

I've got my hands on a VAC Renaissance 30/30 MKIII amp with the Signature circuit upgrade, and now have that paired with a Shindo Monbrison preamp. I'm very excited about both of these! In my opinion, the Shindo has a very nice tube compliment out of the box. As for the VAC, it is currently fitted with the stock tube compliment-Four Chinese VAC-tested 4-300b output tubes, and four Chinese Golden Dragon 6SN7GT low level tubes. They sound quite good, but it seems I can realize some additional benefits by experimenting with the tube compliment there.

Of course one day if I can ever get my hands on (and afford) a matched quad of NOS WE 300b's, I might like to go that route for the output tubes, but let's assume that's not happening any time soon. However, the research I've done suggests you can acheive real sonic improvement with replacement of the low level tubes, at considerably lower cost. So that's where my search and my question lies:

For the amp/preamp setup that I have (my musical tastes are all over the board, but I like a lot of vocal and acoustic-based content. Lots of Blues, bits of Jazz, some rock and electronic. Equal digital and vinyl), what suggestions might you have as a low level tube compliment for my VAC? I have read fantastic things about the Russian military NOS 1578 metal based tubes. I've also heard great things about the Russian 6H8C military tubes (with metal base and black t-plates with holes), which I understand is very similar to the 1578. Other tubes that have come up with favorable reviews in my research have been the ECC32/ECC33 and CV1988 tubes of British origin (Mullard, others), the famous Tung Sol round plates, and the RCA red base 5692's. Most recommendations were that NOS from the 1950's was most preferrable. Does that match with the findings any of you have had in tube rolling with comparable equipment? Keeping my components in mind, are there options above that you would recommend over others? Or others I haven't mentioned?

Of course I know that the "best" sound is completely subjective and based on listener preferences, components, and room acoustics, but I'm just trying to get some insight from folks who may have had more extensive experience in tube rolling, and hopefully I'll be able to use your feedback to form some baseline opinions of my own as a starting point in searching for items that are both hard to find and difficult if not impossible to audition live before committing to. I definitely won't have the money to swap out tubes very often on an experimental whim, so I'd like to start off with what I believe might be ideal for my needs. I know, I know, an audiophile pipe dream... :)

My system will be as follows (literally, I'm *just* getting all the pieces in place):
Speakers: Verity Audio - Finn
Amp: VAC Renaissance 30/30 MKIII-S (Signature circuit upgrade)
Preamp: Shindo - Monbrison
TT: Rega P3, RB300 arm, Benz-Micro Wood SL cart
CD Player: To be upgraded, but currently a Cambridge Audio 640C. (Still looking, but potential frontrunners are the Doge model 6 or possibly a Naim CD5i-2 at this point)
Music Server: Cambridge Audio
Cabling: Auditorium 23 speaker cables, Shindo Silver ICs for preamp-to-amp, and a mix of Siltech, Harmonic Technology, Shunyata, WireWorld, and Ultimate Cables elsewhere for IC and power cord needs (not 100% sure which cables I will re-use with each component yet; have to trial them in different setups).

Thanks so much for your time, and for your insights. I truly appreciate it.

Thanks,
Monte