skootz,
Earlier I mentioned that not all CD-ROM drives are created equal. Some have RCA plugs, newer ones have mini plugs. Some have the plugs for left and right audio jacks on back for external drive cases and newer ones have the mini-din plugs on front for internal or external drive bay use.
You said
"I've been using an Apple 2X CD-ROM Drive. External connected by scsi."
If that is still in its case, my recollection is that you have RCA plugs on back. Those jacks need to have a left and right channel patch cord with red and white RCA plugs on one end and a mini-din plug on the other plugged into the mic port of the computer.
Regardless of model, where you plugged in your speakers is the audio out source from the CD. The audio out from the CD drive needs to go to the audio in port on the Quadra 605. It is just the same as the audio out of one VCR needing to go to the audio in on a second VCR if you were going to play a VHS tape on one machine and record on a second VCR.
The next question is what level of signal is coming out of the jack. There is line level and mic level. Mic level needs amplification and line level does not or needs less. This article:
http://docs.info.apple.com/article.html?artnum=18275
indicates that PlainTalk is line level device tolerant. In other words, you do to have to worry about blowing the audio circuit on the Quadra 605 by plugging in a line level device into a PlainTalk mic port. Otherwise, as a general rule, you do not plug anything but a low power mic into a mic input jack.
So, even if a CD-ROM drive has the higher line level output, the Mac can accept it. Without a line level out of the CD drive, you would most likely need a pre-amp for your speakers to work.
Take a look at the "Ports" listed on these three different spec pages from Apple:
http://docs.info.apple.com/article.html?artnum=112231
http://docs.info.apple.com/article.html?artnum=112217
http://docs.info.apple.com/article.html?artnum=112365
Notice how the 605 page just mentions Mic type as PlainTalk plus a speaker port. The 840 AV lists the same PlainTalk mic and speaker ports but also has RCA video in and out and S video. (No RCA audio input or output plugins - they assume you are going to use the PlainTalk port and an adapter from RCA plugs to mini-din.) If you look up the specs for the 8100 AV, audio adapters are provided. The 8500 included the AV RCA audio input and output ports standard.
Finally, with the 6260, Apple Spec sheets give some specifics:
"Sound Notes: INPUT: impedance 100 kOhm; avg. line level 100 mV rms; avg. mic. level 70 mV rms, max. input level 1.8 V rms>"
All of this boils down to needing something other than the SCSI cable to carry the audio signal. If you do not have a SCSI cable AND an audio patch cable, the signal will never make it to the CPU for processing.
One last bit of information to cover all bases.
If you look at the back of an Apple SCSI CD-ROM drive that is not installed into a computer or external case, you will see the following pin labels, starting left to right. [ 'Audio' pins RGGL (for right channel, ground, ground, left channel) ] [ 'Parity,' 'ID' 012; open pin; open pin; 'TERM POWER ] ['SCSI' 1-50 pins ] and then DC power input with large pins. I believe all CD drives have those first four audio plugs on the circuit board for the drive unless it is so old that it is just a data drive. For internal installations, there will be four little wires wrapped in a gray jacket with a flat four wire connector on each end. That will go from the CD to the motherboard.
On an external drive, those four wires will go from the drive to the external jack on the case. You will never get audio to play on your computer speakers if those four wires do not make it to the motherboard. That is why speakers connected directly to your CD-ROM drive work. They are directly connected to the source.
Jim
