Identify System Bottleneck - Digital Front End or Preamp


Need some opinions on whether to upgrade my digital front end or preamp first.

System:
Speakers:  Wilson Sabrina
Amp:  VTL ST-150
Preamp:  Hovland HP-100
Digital Front:  Mac Mini w/ Audirvana3+ & Ayre QB-9
Cables:  Cardas GR

I'm trying to decide between upgrading the Hovland HP-100 to VTL TL2.5i, or upgrading the digital front end to a Mytek Brooklyn Bridge.  The Hovland HP-100 has been updated (twice) to the latest production specifications right before Hovland went out of business.  I've also recently retubed with super low noise pre-war yugoslavian 12ax7s and super low noise telefunken 12at7s from RAM-labs.  My concern with upgrading the preamp:  Will the VTL tl2.5i actually surpass the Hovland's performance or will I actually loose sound quality?

Regarding upgrading the digital front end:  I can only see benefits, but not sure if this is the bottleneck, or the preamp.

Room is highly treated so there is absolutely no need to address room treatment at this point.
cbl117
I would install audio grade fuses and wall outlets if not yet done so.
David Pritchard
Negative, give me a real upgrade plan. Not hocus-pocus...

Let me restate the ask, again:

"Need some opinions on whether to upgrade my digital front end or preamp first"
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@davidpritchard  gave you good advice, but if it isn't what you want to do, I understand and it's your choice, as is everything in our hobby.

Have you considered trying loaner Cardas Clear Beyond or Clear cables vs your GRs? Might be worth exploring!

I'm not making a statement with respect to the digital front end vs the preamp choice...just that if I were to start the process, I'd begin with upgrading my digital front end, first. And I would explore a number of options (inclusive of the Mytek Brooklyn) that fall within the same budget range.

All the best with your search and choices.