difference between an active and a passive preamp?

The input impedance of your amp is 20k ohms. IMO this is not a great match for a passive preamp. There could be exceptions, but I am not aware of any.

On the other hand you could use a buffered preamp. This uses active circuitry with no gain. The active circuitry greatly minimizes the risk of impedance mismatches. There are tube buffers and solid state buffers. A few solid state options that come to mind are the Pass B-1, Burson Audio, and Horn Shoppe Truth. The latter of which I own and can state that it is extremely fast, detailed, and transparent. It gets out of the way which is what I believe a preamp should do. However, I would not classify it, as well as other solid state buffers, as having a tube like sound.

Also note, not all buffers have a volume control. If you desire something "tubey" you should probably stick to an active tube preamp or a tube buffer with volume control.

I wouldn't necessarily consider a buffered device a band aid for passive-hostile systems. If you look at the designs of a Pass B-1, Burson-160, and Horn Shoppe Truth as examples, these buffered devices are anything but band-aids. They are also technically active devices as the buffers require a power supply, but in general they do not add gain to the system. The main purpose of the buffered output is to provide a consistent and low output impedance, generally under 100 ohms, but this could vary depending on the buffer design. Those using opamps or other solid state devices will tend to have very low output impedance, while tube buffers will in most cases have greater than 500 ohms, perhaps even over 1000 ohms.

IMO optimal dynamics can be achieved with both passive and active buffered preamps, my Lightspeed attenuator, Truth, and Silicon Arts Design preamps being examples in my system. However, system matching with a passive is a bit trickier than an active buffer (which if the output impedance is very low and due to the active circuitry may also provide the benefit of using longer interconnects). To really determine if your system is passive friendly and more importantly if you like the resulting sound, go to Arthur Salvatore's web site and read up on the Bolero test. This should give you a good idea if your source has enough output voltage to drive your amp. If so you might be ready to experiment a bit with resistive, magnetic, or LDR passives, as well as active buffers (preferably those with built in attenuation).

I could go on about how component specs can influence the sound, as can cable length and capacitance, but there is nothing like hearing it for yourself (although I think your system would benefit more from an active buffer). Lots of options out there at very reasonable prices to try both passive and/or active buffers. I know Ed Schilling offers a money back option on The Truth, and at $800 or so it is well worth a test drive. There are others that may offer trial periods as well. Take advantage of those opportunities to listen for yourself.

My need for an active buffer with attenuator is due to a need to run long interconnects to an amp that sits in between my speakers. I have another set-up where I just use the Lightspeed with short interconnects to the amp and long speaker cables. Quite frankly, both units are very transparent. There are slight sonic differences, but nothing to split hairs over.

As for the TAP-X, IIRC the 6 input version John Chapman made has a board where the two sets of outputs can be operated with an active buffer by the flip of a switch. Quite a nice feature.

Another active tube buffer that is getting some attention is from Dodd Audio.

I've got my eyes on the Decware preamp with adjustable voltage. Talked to Steve about it and it is a well designed piece of equipment. Can be an OTL headphone amp as well.

Stan Warren designed some great pieces. The SP100 is one of definitely one of them.