How to Bi-wire speakers when using a subwoofer

Pointless.

It will work but offers no advantage.

"....Depending on your gear, there may be another way to connect your sub that would actually offer benefits to your system..."

OPTION

-- Longer length RCA interconnects direct from your preamp outs plugged into your RCA inputs on your subwoofer.
That way your bi-wire speaker cables from your amp to your speakers remain undisturbed "as-is".

What I did:

I Bought Klotz AC110 bulk cable (10metres) and then had the pair of 5metre lengths professional terminated with Neutrik Profi RCA connectors to serve as the ICs to the subwoofer.

Note: (These are exactly the component parts that the REGA "Couple" ICs are made with, and actually made for REGA by KLOTZ....)

I bought the Neutrik Profi RCA connectors on EBay and bought the bulk cable separately directly from a German cable/ parts supplier ... Much cheaper cuz KLOTZ is a German cable.

I use Nordost Freys as my main ICs and these REGA Couple interconnect clones are no slouches by comparison regardless. They are outstanding in their subwoofer role.

PS:

I bought an extra 10 metres of cable and another pair of Neutrik Profi RCA connectors to serve as a swap-in HT subwoofer cable for my other HT subwoofer , and is as good as my expensive NORDOST HT subwoofer cable.

What kind of speakers do you have? The effects of biwiring can vary greatly. With some speakers, you'll hear little to no difference, and on others just the opposite.

If you want to (or have to) connect the sub at speaker-level, rather than by means of the line-level option Akg described, under most circumstances it would be best to connect the main speakers directly to the amplifier, using good quality heavy gauge speaker cable. That would apply regardless of whether you are biwiring or not. You would then connect the sub to the main amplifier via cabling that could be narrow in gauge and of lesser quality, since active subs draw essentially negligible amounts of current, and since any effects that cable may have on mid and high frequencies won't matter.

If you want to consider connecting at line-level, via RCA connections, there are issues that can sometimes arise involving impedances and cable lengths, especially if the output impedance of the preamp is high and the length of any of the cables that are involved is particularly long. If you want to consider that approach, let us know the make and model of the preamp, the power amp, and the sub, as well as the lengths of the cables that would be connecting the preamp to the power amp, and the preamp to the sub. (I'm assuming you are using a separate preamp and power amp; if you are using an integrated amp let us know its make and model instead, of course).

Regarding the effects of biwiring in itself, opinions and reported experiences are divided. Based on the threads I've seen on the subject, IMO all that can be said is that it may or may not make a difference, and if it makes a difference it may or may not be for the better :-)

Regards,
-- Al