To much high

This weekend I traded my B&W CDM1's for a pair of beautifully finished home-made speakers, comprising a Morel tweeter, Seas (aluminium) mid/low and Seas woofer in a tall housing. I listened to them on a tube amp in a heavily furnished room, and they sounded awesome. Back home (you guessed it....) I connected them to my transistor amp, in a rather hard-sounding room. The low and mid is everything I ever dreamed of, but the top-end is driving me nuts. Since I don't have the cash to change my amp I'm thinking of changing my (silver) speaker cable, or, as some sort of last resort, placing a resistor before the tweeter. Any (other) suggestions?
You can also experiment with spkr. positioning, the most radical being a severe toe in to give you nearfield listening to eliminate most of the room. This should help identify how much the room affects the sound or if it's the gear.

Then again, you can use cables as tone controls.
Ditto to the above. You are wasting your time trying different speaker cables. Try moving the speakers, especially toeing them in. I actually have mine crossfiring about two feet in front of me. Adding room treatment can help too. You said nothing of what your room is like and that is the biggest culprit. Speaker position tweaking costs nothing so is certainly worth a try. Treatment will help more than just the highs.
Assuming you ruled out the source material, if its the speakers, accept it and be more selective in future. If the room is too bright, then first treat the direct reflections: side wall, floor, ceiling.

This is done by placing a mirror on a side wall until an imgage of the speakers appears in the mirror from the listeing position. That is the spot to place an acoustic device (of 2' sq should suffice since the location is so accurate). Try a pillow on a table first, or garment on a hanger, whatever to experiment.

A throw rug on the floor similarly located if the room is not carpeted.

Then try the wall behind the speakers. BTW the greater the reflected distance (path of the sound energy), the less significant its reflection is. When it reaches and exceeds several feet in distance over the direct speaker to listener path, it is no longer an issue.

This can be a useful practice anyway, especially with box speakers, being carful to not over-damp, or deaden the room. Or perhaps it will add enough absorbtion if the room is too bright.

And if I may suggest, rather than prefer some 'sound' quality over another, which is masking the info on the source material, aspiring to 'true to the original' in playback. That is, the best you can do with any system is accurately reproduce whatever in on the recorded material.

With transparent speakers, appropriate setup, and a distortion free amp to power them, you will hear and can then discern the good, the bad, and the ugly, in available recordings.

If however you mask the source with perferred distortion in any component in the sysem, you are also masking any well produced and engineered sonic excellence that may otherwise be available to enjoy as 'live' like realism, which is all the more involving.

The system is a means to an end, is it not. Rather than an end in itself: where you would sit and listen to how 'good' your system 'sounds', and using the music only as means to enjoy the system.

Would not anyone rather than point out to friend how their system sounds, instead not have to point out how real the music sounds: as though it were happening in the room?
"To much high"

Is that different than 'From much high'?

I think you meant 'too'. :-)
I would have to say that the statement of 'wasting time switching cables' is a little off the mark, as cables can greatly impact the overall sound. (Van den Hul vs. Kimber, in general, have totally contrasting characteristics - Van den Hul being warmer/slower vs. Kimber being lively and quick). Having said that, I believe a combination of what was stated in the previous responses can help to finely tune / tone down the 'brightness'. Try placing a large area rug on the floor in front of your speakers. Also, putting some form of sound absorption material on the wall behind this system will greatly help, whether it be a wall-hanging decorative rug or sound absorption material specifically designed for that purpose. Side walls (first reflection point) and wall behind the listening area should be similarly tamed. Some or all of these changes can help to tame the beast and won't break the bank in doing so.