Amps or Speakers which one to upgrade next

What is the rest of your setup??

+1 Randy
A pair of used Quatro's would definitely be in the price range and you'd get a sub, too. Otherwise, I would get a pair of 2wq subs for your 2 sigs.
to fill out the bottom end.
Bob

The rest of my system a Clearaudio Performance DC w/ Clarify arm
Talisman cart. Musical surroundings Nova II and Oppo 103 w/        Ayre Codex
You can check out some pictures under systems 

If you like the sound you have now but want to make it even better, most likely it is a much better amp and source that you want. But I would probably start with tube rolling and trying other cables. Rogue is a value brand, it is not high end.

I daresay if spent wisely you could upgrade your amp AND your speakers for $7K. Perhaps something like this:

https://www.audiogon.com/listings/tube-line-magnetic-518ia-extra-tubes-mighty-845-set-magic-2017-11-...

And since you like Vandersteen you could do this:

https://www.audiogon.com/listings/full-range-2017-11-07-speakers

Though I personally also like the looks of these:

https://www.audiogon.com/listings/full-range-odeon-tosca-gorgeous-german-horn-speaker-2017-11-26-spe...

And these which as an Audio Note owner I can highly recommend:

https://www.audiogon.com/listings/monitors-loudspeakers-2017-11-17-speakers

That was a fun exercise that took just a few minutes poking around the site, obviously just a few things I like our tastes may differ. My best advice would be take your time, do research, listen if you can, and try to buy once and buy right.  Good luck!