Hi Fiftyfifty,
I haven't used the Psvane 12ax7, but used the 12au7 in my Line Magnetic - it worked well in the DAC - a reasonably clear and warm sound.
Now here is where the answers become difficult.
A good 12au7 does not mean a good 12ax7 by the same manufacturer.
In my Leben amp, which is warm, I found that the Telefunken's with their super clarity and relatively low bloom worked best. Mullards pushed it to too warm compared to the stock tube (think nos GE).
So any tube will have to be seen in the context of your system and what sound you want to achieve - hence one fits all solution just doesnt exist, unfortunately.
So the sad answer is that unless you get lucky with your first purchase (you can guess from reading reviews on the net or with generic comments like mine above as long as you know your system's sound well and know what will make the fit) or get a benevolent soul to lend you tubes, you will need to punt.
Vivek