When you ask, 'spending money on the Stratus and upgrading the tubes would be the better route to go with?' You mean versus the Teton? Yes, I personally would take the Stratus with stock tubes over the Teton. The Stratus with some really nice glass is even more of a clear choice over the Teton, to me.
Here's how I feel about it all having been there - if you are rally into the hobby and have been in it for a while don't wast time fooling around with mid-fi. You'll inevitably end up upgrading and have wasted money in the intern. Learn to be patient and save up for what's best. I would also try and find ways to hear the stuff, however, as everyone is different in what they enjoy and listening, not reading, really is the only definitive way. I found when I did a lot of reading, especially early on, I built an impression of what I thought I valued in an audio system. It turned out my preferences were different than what I believed them to be and I only discovered that by listening. Being in Australia you have an advantage because you have some of the most hardcore and experienced headphone users right at home!
The Stellaris is in a league of its own when it comes to amps with only really one competitor - at least of everything I've heard, both more and less expensive. The Studio and Stellairs are both top of their class, but have extremely different characteristics. They truly are an apple and an orange.
When you say, "stuck" I'm not sure what you mean by that... The HD800 is, to me, still the best best headphone, when driven correctly and a few minor adjustments, bar none. It is not, nor ever will be, the bottleneck.