Upgrade Advice Request

New to this sport and looking for some advice regarding next steps in my upgrade path.
Current Set-Up
Source: RoonServer + TIDAL "HiFi"
Pro-Ject Digital S2 DAC/PRE
Onkyo M-5160
Vandersteen Model 1Cs

Love the Vandies and am opportunistically sourcing Model 2s and possibly subs.

Considering several economical vintage options to upgrade the Onkyo, as follows, and would appreciate any insight/counsel you might offer.

AdCom GFA-5503     $300
Hafler DH-500     $360 - $500
Parasound HCA-1500   $400
Bryston 3B         $500
Adcom GFA-5400 (pair) $550 - $700; idea here would be to bi-amp Model 2s

Also - Should I be looking for a pre-amp and if so what? From a functional standpoint, I am good with the S2 PreBox, but I keep reading about sonic improvements achieved with Vandersteens by adding a tube pre.

Thanks in advance for your help!