When you say "two mono amps to each woofer," do you really mean one mono amp to each woofer?

Assuming that is the case, the connections can be made by using a pair of xlr y-adapters, such as these:

http://www.bhphotovideo.com/c/search?ci=4173&N=4289288134+4289360554

However, several things have to be kept in mind:

1)The gains of the amps have to be equal or very close to it, or else you will introduce a level mismatch between the woofers and the mid/hi's.

2)The preamp outputs will see a load impedance which is a considerably lower value than the input impedance of each amp. If the input impedances of all of the amps are the same, the preamp will see a load impedance equal to that value divided by 2. If they are not the same, the combined input impedance on each channel is the product (multiplication) of the two input impedances, divided by their sum. That number should be at least 10 times greater than the preamp output impedance, at the frequency at which the preamp output impedance is highest (which is usually 20Hz, especially in the case of a tube preamp). Otherwise a frequency response imbalance, such as deep bass attenuation, will probably result.

3)Low capacitance cables should be used, especially if the runs are long. The signal getting to EACH amp will be affected by the sum of the capacitances of the cables that are connected to BOTH amps. If that total capacitance is high, and if the preamp output impedance is high at high frequencies, upper treble rolloff will result.

Regards,

-- Al

Assuming that is the case, the connections can be made by using a pair of xlr y-adapters, such as these:

http://www.bhphotovideo.com/c/search?ci=4173&N=4289288134+4289360554

However, several things have to be kept in mind:

1)The gains of the amps have to be equal or very close to it, or else you will introduce a level mismatch between the woofers and the mid/hi's.

2)The preamp outputs will see a load impedance which is a considerably lower value than the input impedance of each amp. If the input impedances of all of the amps are the same, the preamp will see a load impedance equal to that value divided by 2. If they are not the same, the combined input impedance on each channel is the product (multiplication) of the two input impedances, divided by their sum. That number should be at least 10 times greater than the preamp output impedance, at the frequency at which the preamp output impedance is highest (which is usually 20Hz, especially in the case of a tube preamp). Otherwise a frequency response imbalance, such as deep bass attenuation, will probably result.

3)Low capacitance cables should be used, especially if the runs are long. The signal getting to EACH amp will be affected by the sum of the capacitances of the cables that are connected to BOTH amps. If that total capacitance is high, and if the preamp output impedance is high at high frequencies, upper treble rolloff will result.

Regards,

-- Al