How do I get the best soundstage?

Speaker setup plays a big part. Do a search for Sumiko Masterset and give it a go, all it will cost is time.

Cartridge wise a Transfiguration isn’t a bad place to be but when setting up a unipivot arm measure VTF at record surface height, or if you can’t accept that it will measure higher than it plays and use your ears, just using the measurements for reference.

Something better than a project phonobox might be a good move, if the Pass has a built in MM stage consider a SUT but if it doesn’t there are some fine stages out there.

Volti keep saying their speakers are fun, are you having any?

Sell the Volti’s and get Ohm Walsh’s. 3-D room-filling sound from any listening position! I have a pair. An astonishing speaker! Nothing else will make as big a difference!

Speaker placement.

I second that you should spend as much on a phono stage as the TT + cartridge… the Phonostage is critical in imaging. I would recommend looking at Audio Reseach  PH8… or the best used you can get in that series. I had a similar table and the sound (and transparency) increased dramatically with each PH upgrade. Presto also  get great reviews… but I think ARC wins for durability.

Speakers and placement are critical. If you haven’t point them to cross about 18” behind your listeners seat. Then slowly decrease the toe in. The soundstage should slowly expand. You want to go out until just before the central image starts to weaken.

As @yeti42 said, try the Sumiko Setup.  These are the instructions I use: https://www.audioaficionado.org/showthread.php?p=979168

You're not going to get it on the 1st, 2nd or 3rd try but don't get discouraged.  I have the patience of Mike Tyson losing a boxing match and I was able to stick it out and get it mostly right.  You'll try it and not really hear much difference the first few times. Then you'll have an "ah ha" moment. After listening for awhile longer you'll realize it was just an "ah" moment but now you know something is different. A few more tries and you'll get it. Best bass doesn't mean loudest, it means sound pressure; you can feel the difference.  At the end the speakers may not be the same distance from the front wall or even the exact same toe in. Some people can't stand this and just give up. That's ok. It's not for everyone. At least you'll get a taste of what you should be looking for regardless of your setup method. My local dealer uses this on all his demos. He doesn't even put marks on the floor. He sets the speakers new up every time. Once you get good, it takes about 15 minutes to get most of the way there.