Bryston options

Why replace the Bryston if it is working fine and sounds very good? I have an even older 3B that is working trouble-free!

There is a Bryston 4Be listed here. You can connect the Lumin to it for volume control.

I'm planning on replacing the Bryston because things have moved on over 20 years and because I now have both a far better source and better speakers.  The Bryston is brilliant but I think its now the weakest link in my hifi chain...

The new Bryston Cubed series amplifiers are a significant improvement over the older models. I have met a few people who prefer the older models over the Cubed series, but it's rare. So I'd certainly give that option some consideration. With the Martin Logan Vantages, you'd want at least the 4B3 for sufficient drive capability, but you'd probably even benefit from going with a 14B3 considering the Vantages low impedance at some frequencies.

Otherwise in general I think the load demand from the Vantages is going to be your biggest issue in terms of amplifier compatibility.

The first generation Bryston amps (such as 9B) were okay, but somewhat dull sounding.  The newer generations (SST, SST2) were much better resolution, but they had a tendency to sound dry and sterile.  The newest "cubed" series is the best so far and sounds rather sweet in comparison to the older SST2 series. 

There are definitely other brands to consider for an integrated (Krell, Kinki Studio, etc.).

I'm hoping someone will opine regarding the Lumin amp.. there are very limited reviews and no one seems to stock it..

@grahamsphillips we have the Lumin AMP here, by default paired with the Lumin X1. I'm afraid I don't have a good idea of how well it will drive the Martin Logan Vantages which is a relatively difficult load.

The sound quality is very good but you need to be aware of the sound character Lumin has chosen to present. It is also much more expensive than a similarly powered Bryston amplifier.

I have he BP17 cubed preamp and the 4B cubed amplifier. An awesome pair . 
(Traded up from the BP-26 preamp and 4Bsst2 amplifier.)

I listen to chorales, operas and other sources where the higher frequencies - - specially the female voice - - can make or break the experience.  The BP17 and 4Bc will be very, very difficult to beat.