I spoke to Jenson and was advised that the most appropriate unit for my needs would be the PC-2. it is a 4:1 ratio and therefore would satisfy the needs of both the preamp and poweramp - the preamp seeing a load of 34k ohms and the power amp 225 ohms.... The PI model that you mention would result in a 23.5k ohm load on the preamp and 4.65k ohms on the amp, which if i'm understanding correctly, is less than ideal (ratio of 5:1)
It's not quite that simple, although the conclusion is essentially correct.
The input and output impedance numbers shown in the Jensen datasheets are based on specific source and load impedances ("test circuit 1" shown at the bottom of page 2 of the datasheets), and will vary considerably depending on the output impedance of the preamp and the input impedance of the amp. In this case the balanced input impedance of your amp happens to correspond to the test conditions shown in the datasheet for the PI model, so the 23.5K figure is applicable. But the output impedance of your preamp is much higher than for the test condition shown in the datasheet, so the source impedance seen by the power amp will be considerably higher than 4.65K.
It is important to note, though, that the key concern is not the relation between those two numbers, but the relation between the load impedance seen by the preamp (23.5K in this case), and the actual output impedance of the preamp, at the frequency for which it is highest. See the last paragraph below for further theoretical explanation.
The numbers for the PC-2 (you would want the PC-2RX specifically, assuming that you want to use the XLR inputs of the amp) are based on source and load impedances that differ even more widely from those of your components, and also differ widely from the test conditions of the PI model. That said, though, the PC-2 does appear to be much better suited to your purposes, as does Steve McCormack's Interocitor.
Keep in mind, however, that a volume reduction goes hand-in-hand with the impedance transformation you are trying to achieve. That is specified as 12 db for Steve's unit, and typically 13.6 db for the PC-2. If without the transformer you would be using the volume control in the upper third or so of its range (roughly speaking) that would be a concern. On the other hand, if (as is common these days) you have too much overall gain in your system, and use the volume control in the lower part of its range, that would be beneficial.
The theory involved in all of this is that for an ideal transformer (no practical transformer is ideal, "ideal" meaning among many other things that the DC resistance of the windings is insignificant) the ratio of output voltage to input voltage corresponds to the ratio of the number of turns in the secondary (output) winding to the number of turns in the primary (input winding), while the impedance transformation corresponds to the square of that ratio. It appears that both the PC-2 and the Interocitor have turns ratios of roughly 4 to 1. So the power amp would see an input voltage roughly equal to 1/4 of what the preamp is putting out, which corresponds to a 12 db reduction. The preamp would see a load impedance that is roughly 16 times as great as the input impedance of the power amp. The power amp would see a source impedance that is roughly 1/16th of the output impedance of the preamp. I use the term "roughly" to take into account DC resistances of the windings, various other causes of "insertion loss," variation of the actual turns ratios from the 4:1 nominal value, etc.
Best regards,
-- Al
