So damn hard deciding which tube preamp to buy!

This is really tough.  No one has them in-stock.  All special order.  The key is finding the right feature set and read some reviews.  In that range, it is tough for something to go horribly wrong.  It is not like you are going to get an ARC, VAC or AVM preamp and you are going to say, my god, this is crap.  

The critical thing is make sure that it is compatible in advance with your power amp.  Biggest issue is going to be an output impedance and/or gain mismatch.  After that, rely on the house sound and favorable reviews.  

This is part of the reason I am such a big fan of AVM.  The flexibility to tweak the preamp with different cards and to adjust the output makes it much more flexible than most. 

One option might be at least see if you can get store credit back if you really hate it.  There are usually restrictions.  You will be stuck with what that retailer sells, usually restocking fees, etc... But it is better than losing 50%+ on a device you want to resell that you hate. I customize those things based on the order.  

The AVM PA 8.3 - Seriously.  With a tube output stage, two sets of RCA & XLR inputs with tone control and the phono stage is $23K.  Add in SS output stage for a subwoofer and it comes in right at $25K.  

This is truly a world class preamp.  It is unbelievably quiet. Neutral to warm and AVM delivers a massive soundstage.  I have had the flagship monos that go with this here and they easily could be mistaken for VAC or VTL gear, just 1100 watts.  It is worthy of the price.  

Know that Udo (the owner of AVM) was at Burmester for a long time and has an incredible track record.  

This article explains it pretty well.  
http://www.moxtone.com/Tube_buffer_en.html

BAT uses tubes in the rectification (power supply) vs a SS rectifier.  This is technically a quieter approach.  My experience is that in practice, this is only really critical with highly sensitive speakers.

They then use tubes in the gain/amplifier stage and the buffer.  Alternatively, Conrad Johnson uses two 6922s in the amplifier stage and then MOSFETs in the buffer so yes, this is a hybrid approach.  
Many companies take very different approaches and each designer often has very firm opinions on what does and doesn’t make a good tube circuit.  
I have had one designer tell me a 6922 is not appropriate for audio applications.  I have other designers where it is their preferred tube.  

The important thing is picking a preamp that will marry well with your power amp.  

Sorry for taking time to get back to you on this.  Was with family at the beach.  
You want to have the right amount of gain, output impedance.  Get those right and the amp will sound great.  If you have too little or too much gain, sound will be bloated or thin respectively.  If the impedance is wrong, then you will issues.

this is a great write up.  
https://forum.audiogon.com/discussions/how-to-match-preamp-and-power-amp

I would stick in the mid teens, 12-18dB of gain with your power amp.  200/100ohm balanced/unbalance impedance range should be good for your amp.  This doesn’t need to be exact and some deviation is allowable.