Do I really need a preamp?

Mapman is right with proper mating with passives.

And as I have stated many times.

If you decide to give a 10kohm passive a try, such as the very affordable $49.00 Schitt SYS passive pre. http://schiit.com/products/sys-passive-preamp,
the only proviso to look for to give them a great match are.

1: Interconnect to power amp to be low capacitance (<100pf per foot) which most good quality one are, and 3mts or less long.

2: Tube output sources can be a problem if higher than 1kohm output impedance, solid state sources are normally never a problem.

3: Input impedance of the power amp should be 33kohm or higher, which most are (47kohm being the standard).

If you have these, which 99% of systems are, then you can reap the benefits of the transparency and dynamics that a passive will bring to your system.

Cheers George

George is mostly correct here, just watch out that some solid state amps have a 10K input. 47K is not a standard.

Out of a 4V source, I have heard a Goldpoint resistor type passive preamp sound pretty good into Class A, SS monos with 100K ohm input, but still lacking depth and dynamics compared to the same amps played through my preamp, which is buffered with no gain. Into NC1200 Class D amps, the passive preamp sounds very clean, and delivers close to the same level of dynamics as I achieve through my buffered preamp. However, through my Class AB SS stereo amp with 10K ohm input, the passive preamp sounds terrible.

I also have a pair of balanced Endler attenuators, which connect directly to the amplifiers so there are no cables required after the attenuators. I cannot discern any significant difference in dynamics between those and the Goldpoint passive, from which I use a1M cable into the amps.

Marqmike, I would think first your power amp has enough gain
for a passive preamp to work very well, this would be a very
important thing. Second you must have a very good quality
passive preamp, passive preamps like active are not all
created equal. I have had high quality amplifiers that they
could carry an inferior preamp and vice a versa. Get both
right and your in for a treat. A few years ago I owned a
McCormack DNA-1 with a revision A which had plenty of gain
for a passive preamp coupled with an upgraded McCormack
passive preamp. It sounded heavenly, there was no lack of
dynamics, it was refined and transparent as hell. I miss
that combination terribly because I never thought of looking
at another active preamp with this combination.

I believe even in Stereophile John Atkinson states 47k-51k input impedance has been an unofficial input impedance standard now for over 50 years for most home audio S/S products input resistances. Since it was made the standard for MM cartridge loading way back and they followed suit with preamp and poweramps at 47k-51k.

Tube amps have even higher up to and higher than 100kohm which is even better for higher value passives like 20kohm ones.

As for the very few amps that are 10k that many tube preamps won't drive, they constitute probably less than 1%
of the market share.

Cheers George