Hi Matt, and welcome to the forums!

I would not use a commercial jack-phono cable as they use TS jack plugs that would place a short circuit to ground on the negative lead of the 1641 balanced outputs. Although doing this would be unlikely to cause permanent damage to the Tascam unit, it's not a kind thing to do, and will certainly produce extra heat dissipation, and could well cause distortion on peaks on the positive output as the drive amplifier chip and power supply pour current into the short circuit.

There's a proper way to do this and there are various cheap ways that may be worth trying first. The cheap ways mostly involve wiring or building up your own pair of custom jack-phono leads.

If you are not handy with a soldering iron, move on to the next paragraph. Otherwise, buy a single phono-phono screened lead of twice the length you need to go from the 1641 to your monitors, and also buy a pair of TRS plugs. Cut the lead in half and solder each cut end to a TRS plug so the that cable inner core goes to the TRS plug's tip connection and the cable's screen goes to the sleeve (outer) on the TRS plug. Leave the ring unconnected. This will give you a clean signal of nominal -2dBu level to your speakers. The speakers should be able to handle this, but it is possible that even this level will overload them, in which case you will need to come back for some advice on wiring attenuating resistors into the TRS plugs.

If you don't want to do any wiring of your own, you could go along to Radio Shack and get a pair of phono-phono leads of the right length to go from the 1641 to your speakers and then a couple of [[url=http://[/URL]="http://www.radiosha…"]these[/]="http://www.radiosha…"]these[/] TRS jack plug to phono socket adaptors. Use the tip output of the adaptor leaving the ring output disconnected. I can't tell from the RadioShack photos, but the adaptor may be marked L and R, in which case use the L output. You might still have the problem of overloading the speakers, but it's worth trying for the relatively small outlay involved.

Let us know how you get on.

Thank you very much for your swift and detailed reply! I'm pretty sure I can handle a bit of soldering, so I think I'm gonna give that a shot.
By single phono to phono, do you mean a lead with just one plug at either end like:

[[url=http://[/URL]="http://www.amazon.c…"]Cable Mountain 5m Gold Plated Single RG59 Coaxial Phono Cable for SPDIF/Digital Audio and Composite Video Cable[/]="http://www.amazon.c…"]Cable Mountain 5m Gold Plated Single RG59 Coaxial Phono Cable for SPDIF/Digital Audio and Composite Video Cable[/]

or a standard dual phono cable that's twice the length between the tascam and the speakers? Because if you meant the dual one, I'm confused as to why I'd need one double the length.
Also the speakers themselves have a volume control on the front, so am I correct in saying overloading shouldn't be a problem as long as this is kept down to a suitable volume?
Again, thanks for the reply, and as soon as I can get the components, I'll give this a go and see what happens :biggrin:

Getting a single double-length lead and cutting it in half is just a trick to keep the cost down, so the first one you referenced would work, but it's a bit over the top. There were others listed at the bottom of that page that may be more appropriate for audio use, but I would not go as low as the second cable you linked to.

You don't mention the type of active speakers you have, so I have no way of knowing whether the built-in volume controls are at the input (in which case they will deal with a high signal level) or after some input buffering. If the latter, the input stage may overload before the volume control can cut the signal down, so that's the case in which you may have to fit attenuators in the input lead. Try it first with just the cable.

Thanks again for the advice, I went and got myself a cable between the price range of both those links.
Now I need to think about those TRS plugs. Since you said to leave the ring disconnected, could I just use some TS plugs that I found lying around in my house? would save me going to get some more (not that they're going to break the budget :P)

And about the speakers, I would have told you a lot more, but I can't seem to find out anything about them - they're too old to have a place on the internet, I think!

No, I'm sorry but the whole point is to use TRS plugs so that the ring contact can be left disconnected. If you used a TS plug, the ring contact in the socket would connect with the sleeve on the plug, thereby grounding it and shorting the -ve output. If this were an input we were considering, then a TS plug would be fine as the -ve terminal of a balanced input requires to be grounded when using an unbalanced source.

Thank you very much and sorry for my poor understanding of this - I've got some trs plugs now so as soon as the RCA comes through I'll let you know how it goes. Thanks again!

EDIT:
Ok, Update, after soldering everything, tested the leads and they work perfectly with no overheating and totally clean sound. Thank you very much!!