Have you had a previous set up that did have that magic?
Are you sure that it's the amp that isn't doing it for you? I know for me it's my bass guitar plus amp plus cab in combination with my playing technique that create my tone.
I use several heads (Markbass, Trace Elliot, Orange) through either ceramic Bergantino or Markbass neo cabs, and whilst there are differences, all combinations sound essentially alike. I attribute this mainly to my choice of bass guitar and playing technique. The next biggest difference would be down to the cab, with the amp last.
Most modern amps can be EQd to a nominally flat profile and then adjusted to almost any desired character. I've never played a Subway 800 but I imagine it's extremely capable; maybe see if you can try some more colored preamps/DI pedals in front of it before swapping out?
I add tube warmth to my Markbass heads with a 12ax7 based compressor; subtle but in combination with an HPF is perfect for me. More extreme tones can be achieved with my Tech 21 VT and Paradriver pedals, but I rarely do.