Cited from NetBSD/pmax's page:
"DECstation and DECsystem 5000/240 and /260 systems (codename 3MAX+)"

So what's 'serial console 4MAX+' mean?

Hardware info of my machine:
  >> cnfg
3: KN05    DEC  v2.1k  TCF0  (32MB)
                             (enet:08-00-2b-39-c5-2f)
                             (SCSI=7)
1: PMAG-DA DEC  v5.3g  TCF0  (PMAGB-EA: PXG+ -- D=24)

I'm using a 3MAX+ with PXG+ video console and R4400, right?

Besides, I see this in 1.5_ALPHA2/INSTALL.txt:

    Supported devices include:
    o   DECstation 5000 series TurboChannel video
       -   PMAG-E (PXG+) 3D 24-bit accelerated frame buffer.