Power and Pre amp HELP & Recommendations needed.

I want to switch to a power and pre setup. I have a Rotel RCD991 cd player and I have B&W Nautilus 804 speakers. I would appreciate any recommendations and advice on pre and power amp combos. I have $4000 to spend therefore I guess that means $2K for the power amp and $2K for the preamp.

I am looking at used gear. To date I have used solid state gear. I have heard several inexpensive tube preamps such as the SFL1 signature and was not impressed however I am open to trying a tube or SS preamp with a SS power amp.

Some questions I have are: Is it important to stay with the same manufacturer for synergy? Can you mix a tube preamp with a SS power amp? Advantages of tube vs. SS vs. digital power amps? Is it better to buy one powerful amp or two less powerful amps and use a biamplied set-up?

I listen to jazz most of the time at low to medium volume.

Any recommendations or advice would be appreciated.
Thank you
Too many of (your) questions will be unanswered! All these questions are same as to asking this forum, what kind of furniture you ought to get! I can point you into the (right) direction by suggesting you to go tubes! Only tubes will re-create the midrange magic! For listening acoustic instuments, at least. Preferably push-pull class "A"!
The one thing I would question is your need to go the separates route. With a $4000 budget, you're in a difficult range where a combo of separates may not be better than a really good integrated.

In fact, for $4000, I can't think of too many separate combos that would clearly trump an LFD Mistral or Plinius integrated. Both of those you could get brand new and still save at least $1,000, plus you would need one less set of interconnects ($100-500) and not have to worry about preamp/amp synergy.

I'm sure you'll get a recommendation about using a combo with good passive preamp, since they are much less expensive. In theory, you can get more performance for the dollar going this route, but it's unconventional and tricky.
Here is my suggestion- 750.00 will get you a used Adcom GFP 750. This is a great preamp. Spend 2K on a used Classe 200. Actually 2K will get you a used Krell,Levinson,etc. Spend the last 1K on interconnect and power cords. Matched with your Rotel and B&W's this would be a kick ass system.
Well, it looks like you started building your system at the speakers and are working to the front. The Nautilus line is in my opinion a bit overkill for $4000 worth of amplification. I have the N803's with $8,000 of amplification and a $2,500 CD player.The 803's are way too revealing for the CD player but magic happens when i listen to them with my $6,700 analogue front end. The sound has always been lacking in any system I've owned where the speakers are as pricey or pricier than the front end (or amps). You would not believe how harmonic and rythmic music can be from just a small pair of $1000 2-ways with 10Gs of source and amplification wired up. If youre spending that much for N804's i don't think you'll be moved until you put about 3500 in a CD or TT front end regardless of what amps you use. you'll have volume, but no musical order and pace.
I humbly suggest you check the archives.
I would check out a top shelf integrated at that price. I would recommend the BAT VK-300xSE or the Rowland Concentra. They both give you 150 wpc. If you need more power, then I would go seperate. It is not critical to stay in the same family for seperates, IMHO.