In my opinion, there is no such thing as an amplifier that's "too big"; only big amplifiers turned up too far. On the other hand, amplifiers can easily be too small – and deliver unwanted and potentially disastrous results.
The lesson I learned: When we introduced the Walsh 5 Limited Edition in 1988, it was the best speaker we could make at any price. Our philosophy was if it either sounded better or measured better, we went with it. To present them at a Consumer Electronics Show, I borrowed a Crown Macro Reference power amp. We have used Crowns in the lab for years and years and this was their top-of-the-line audiophile amp. The speakers sounded wonderful and I recommended the amplifier to many customers as a great match. One consumer bought the Crown and the Walsh 5s and proceeded to blow up the Walsh 5s on an opera recording. Now, we, at the factory, had never blown up the Walsh 5's inverted driver before. This was really something. The consumer sent the Crown back to Crown to be checked out and the speakers back to us to repair. When Crown reported no problem, the consumer had the amplifier sent to us so that we could try and repeat the event -- he even sent the CD and told us where the speaker failed. We tried it at a good listening level and fried the replacement drivers. Crown has Input-Output-Comparators (IOC) lights to indicate when the amplifier is clipping (being driven into high distortion). I had noticed a few flickers of the IOC and had not turned the system up louder. They went on solidly during the passage that burned out the speakers. I talked to a Crown engineer to determine exactly how much power the amplifier was producing when the IOCs light up. It was 3400 watts in the 4 ohm load of the Walsh 5LE's!
Now from this experience, you might think a 3400 watt per channel amplifier is too big for the Walsh 5LE's. No, it was just a big amplifier turned up too far. When the customer received his whole system back, he was totally satisfied and just turned things down a little if he noticed the IOC's flick on. He never harmed another speaker.
The advantage of very big amplifiers is that they play loudly without clipping on transients. Clipping usually sounds very harsh and unpleasant. It also tends to blow tweeters since the distortion produces even greater energy in the treble range.
The two downsides of a very big amplifier are:
1. the temptation to crank-it-up and see what the system can do and
2. added noise at normal listening levels. You should be certain to listen for noise at 1-10 watt level which is a typical power output level on popular music.
With the reviving popularity of tube amplifiers and the new popularity of little amplifier modules, some enthusiasts are curious and want to try these "new" amps in their systems. The current crop of tube amps tend to be of the low-wattage units. This can create problems.
The size of amplifier you will need will depend on how loud you want your speakers to play, how close will you be listening to your speakers, how sensitive (the ratio of how loudly the speakers play with one watt input) and how musically the amplifier distorts (clip).
Tube amplifiers clip in a much more musical manner than most solid state designs. My rule-of-thumb is you need three watts of solid state power to sound as clean as one watt of tube power. There are exceptions. NAD provides solid state amplifiers with soft clipping on high dynamic peaks. Their 20 watt amp sounds like most 100 watt solid state amps.
My first system had a Dynaco SCA 35 (17.5 watt per channel integrated tube amp) driving AR 4x with an AR turntable with a good Shure cartridge. The amp drove the speakers to levels my neighboring students complained about. The "rich kid" down the hall with a McIntosh 275 and AR3s had a better sounding system; but it didn't play that much louder.
Today, I expect a small tube amp, 8-12 watts, is what is needed to drive Ohm Walsh speakers to modest levels in smaller rooms. It also varies with the Walsh model. The MicroWalsh needs almost twice the power to play at the same levels as the other Walshs. This is because we gave up sensitivity to get deeper bass from the tiny speaker. An amplifier is "too small" if it has to be driven into audible distortion to achieve the desired sound levels.
Enjoy & Good Listening!