I did the same thing. I'm fairly new to all this, and it's my first set up.... so this is For what it's worth.
I just saw Iron Maiden..btw.. awesome. And I have no trouble with Metallica. Much easier to listen to with a tube preamp. Off topic, but "Mobile Fidelity" just released an audiophile/tube remastered from analog tapes pressing of "Kill em'all" and "Ride the Lightning". Very exciting.
I was concerned about the same thing and went this route for the same reasons as you. So far so good.. voices sound very sweet/front and centre, projects right at you, and imaging 3D is much better, snare drum, double bass distinct. Listen to it all day, no stridency with the wailing guitars.
I'm sure you know all this, but with impedance matching, there is a general rule of 30 to 1..output impedance of preamp to input imp. of amp. Supposedly the higher the better. Not a deal breaker though with a mismatch. Supposedly you would just get high and low freq. roll off.
Although, my current preamp/DAC is 3K and I just paired it with the power section of my integrated that is only 20K (while I'm waiting for monoblocks with 100K imp). Complete/gross mismatch, but it sounds pretty darn good...
All the brands mentioned above are a definite step up from what I'd buy. They are very popular....but expensive.. I suppose you get what you pay for, but budget has dictated that I look for (a lack of a better term)... "giant killers".... with cables and power cords etc.. not to mention your front end.. gets expensive quick.
You might want to check out pure "class A" power amps. All the warmness of tubes, but solid state, a happy medium. Tons of slam and dynamics....supposedly.
Something like the Clayton amps (S40 or M200), they're expensive but hold their value. Huge power supplies.
For preamps, go to the audiogon review section and read up on the "TAD 150 signature".. a lot cheaper compared to the above mentioned ($800). With remote and phono stage. <1k output impedence, easy to pair with.
I have a Monarchy M24. It's a discrete designed (2 separate power supplies) tube DAC with a linestage. About $750. Read the Bound for Sound review of the M24 to get an idea (note: not the NM24):
http://www.monarchyaudio.com/
Clayton Class A power amps and Monarchy hybrid power amps:
http://www.boundforsound.com/reviews.htm#Clayton%20Audio
http://www.monarchyaudio.com/BFS_SE160.htm...
(not in production anymore, last month I called Monarchy and they had a European version they built for someone but never bought for !500/2K a pair).
http://forum.audiogon.com/cgi-bin/frr.pl?rprea&1114874904&read&3&4&
(no longer in production, hard to come by..but they do show up used on audiogon)....
This might not be too helpful for 220v/used... but not bad reading. Take it easy.
