I won't grapple with you about the Powerstage 170. Spec is as follows: POWER:170 W at 4 Ohms (
https://www.seymourduncan.com/power-amp/powerstage-170) so if it is in fact seeing an 8 ohm load, you're getting a lot less than 170 solid state watts, which isn't much for bass IMHO. But if it works, it works...all good.
A clean, full, bright tone should be pretty easy to get. I'd start by bypassing everything in the signal chain, and have a close listen to what the bass sounds like, as well as noting how loud it is with no other processing. This is an important step since you can add a TON of gain when you start building up a number of blocks. This may be a source of the over-processed, muddy sound you describe. You don't want your processed tone to be wildly louder than the bypassed tone. Start with you Powerstage 170 set to "flat", and keep in mind that the Powerstage was designed first and foremost with guitarists in mind, not bassists, so the amp itself may have some baked-in voicing that works better on guitar.
From there, start with just the amp block and work with the basic tone and amp gain parameters. If you want clean, then be sure that the initial input gain is set low so there's no preamp overdrive distortion. Or you could use a different amp type that is designed to be clean by default. IIRC, the Mesa bass amp is pretty clean in general.
If the tone sounds too bassy or muddy, you may want to work with the high pass filter to clean it up. If you're able to get a satisfactory ballpark tone, then you can start adding the other finishing touches. Remember, the amp block has its own compressor, so you may want to utilize it before a dedicated compressor block (Master Volume needs to be set fairly high in order for it to work noticeably IIRC). Too much compression in FRONT of your amp can also result in a sound that doesn't "breathe" like you'd expect, and compression on bass is a totally different animal vs. guitar, so be careful with this also. Again, you're starting point with every block you use should be so that it has a relatively neutral impact on the core tone. You can always go crazy from there.
Many drive blocks will frequency limit the sound of the bass. Again, be careful with this, and if you're using it to enhance a clean tone, you'll need to either select one that is designed for clean/boost, or tweak the settings so that it's not doing its own squashing to the tone.
I've used my AxeFxII as the preamp to my SVT 8x10 cabinet (powered by a Crown Xti4002 - tons of power) and the experience was really good. Not exactly the same as my SVT Classic tube head, but I'm probably the only one who could tell the difference. It did take a bit of work, though, no lie.
Hope this helps.