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
The Pre-amp is the heart of your system, The Power amps is the muscles. 

Try to see if you can get a MP-3 Atma-sphere pre-amp or a MP-1 (If funds permit)

I would go the opposite way than what audio doctor suggest and focus on getting a better pre-amp to start and than move to the Digital Front End.
Phantom av the Hovland pre was designed as a reference preamp by the guys who bullt the hoviand capacitors.

This was an exceptional preamp.

We sell lumin and Mytek the T2 is just better.

Dave and Troy
Audio Doctor NJ Mytek and Lumin dealers
Speculatively speaking, the answer to your question is the digital front-end, particularly the mac / audirvana, followed by the little Ayre.
Before you change anything, however, I strongly recommend you try a "regenerating /reclocking" device (many of those around, I use this one) —a very good thing to have when you listen to a digital source. Most of them are inexpensive and well worth the outlay. BTW, I'm familiar with your equipment except for the cables; great choices!
Good luck!
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