Hi Norman,
I have to admit I'm not up on valves/tubes either, I rely on reviews and advice from others.
I'm not averse to selling the Seimens valves but they're not cheap, I'm waiting to hear from the person I bought them from as I can't remember what I paid for them.
As soon as I know I'll let you know how much they would be with the Velleman.
Note: the Valvo tubes that came to me with the Velleman are pretty decent and are a decent stepup from cheapies. They were added to the pre by the previous owner. I don't think you'd be disappointed with them to start off with, then..... the sky's the limit with tube rolling.