Guys, let's not overlook the basics.
First of all, if your machine sounds fine in 4 channel mode, but attempting to use 8 channels sounds awful, then it's not down to bad capacitors. Though having a 20-odd year old machine re-capped is not in itself a bad idea.
If, like me, you use OctaMED SS for many years, you may have forgotten that legacy 5-8 channel mode has some severe restrictions:
1) The channels are not independent and share hardware volume controls. That means that any volume changes in channel 1 also affect channel 5 and vice versa.
2) The legacy mixing routine used to play 2 samples in one channel runs at ~14kHz or so (I can't remember, but later versions of OctaMED had a "high quality" mode that ran at 28kHz but needed more CPU power). This will add lots of aliasing noise to samples that otherwise sound OK when played in 4 channel mode.
3) Sample loop lengths are heavily quantized. Instead of being able to define loops that are as short as 2 sample points, you are restricted to something like 200. This affects both the starting position and the loop length.
4) The biggest killer of all. The instantaneous amplitude of summing any two samples together on a channel may overflow the 8-bit range, resulting in heavy distortion. The mixing routines don't clip the result of adding the two sample values together, it simply overflows, often with sign inversion. It doesn't matter what you set the hardware channel volume to. The only way to properly cope with this is to alter the sample volume in the sample editor. Typically, you'd halve the volume of all your samples in 8 channel mode so that any combination of any pair of samples at once would never exceed an 8-bit result. This effectively means you are now dealing with 7-bit samples.
So, if 8 channel mode sounds awful, there are plenty of things to check. Making an 8 channel MED module sound good is not a trivial task and requires a good understanding of how it all works.
Often, your best bet is to use 6 channels. Not only does this reduce CPU load, but it gives you 2 regular channels on which you can play sounds that are just too distorted by being played by the old mixer.
