Amp - preamp or integrated

you need sufficient room for them

??? Not all mono blocks are monoliths. 

Thisall depends on your budget , a sound ruleof thumb 
less then 25% of the piece of electronics goes into the build,the rest overhead and dealer markup.  A  great integrated has several advantages  such as 1 less pair of interconnects, power cords  and seperate wiring . My brothers Gryphon Diablo is a Perfect example of excellence. There are many excellent integrated amps 
from Denmark  my $6500 Gato 400S was a steal and can match seperate ofmuch more monies.  Pass Labs make a very good integrated in their new line . What is your budget $6k $15$?
please remember respectable interconnects and extra power cord 
is probably $1500-$2k alone .itisthe Parts Quality thst counts .
ifunder $10k the Pass Labs Reno Hifi sells demo,or open box with a full warranty and save several grand.dependingon your Loudspeakers efficiency . Pass has high power, as well as low power models let others know  about your speakers to help you better . 

Lobinero, I have the Vandersteen 2CE Sig II and I’m driving it with the McIntosh MC601 monoblocks (600 watts) and the McIntosh C2300 Tube preamp. I which I could have come over and listen to my system because I reall swear by this kind of set up, it’s overwhelmingly sweet sounding like live music and the sound stage is deep and wide, the speakers disappear most of the time depending on how good is the recording. I highly recommend separate amps and preamps.

Have you changed the tubes in the pre section? Very satisfying and worthwhile changes.
What is your front end? table, DAC, etc? Look there for upgrades.
Interconnects, speaker cables?
And the biggie ....room treatments.

Yes I own the Cronus Mag II it's quite excellent here.
I will never go back to separates. One of the biggest improvements I made in 5 years was the room treatments. GIK Acoustics.

The Vandies may be a little laid back wake them with the tube changes.
I owned these years ago and were very good.
Just my opinion of course.

First thing is keep in mind that there are integrated amps that are designed as separate amp and preamp within one cabinet. If you go with an integrated amp, put that high on your list. I’ve leveraged that with my two NAD integrated amps wired to bi-amp my speakers. Your choices of configuration are just as unlimited as with separate amp(s) and preamp.