There is a formula for determining what roll-off point you want for your bass. I'll try to do a search later to give it to you. Besides the input impedance of your amp, which in your case is high at 145K ohms, you'll also need the output impedance of your preamp to insert into the formula. As to bypassing or paralleling your preamp output caps, I wouldn't recommend it. I have several reasons for this opinion. I would firstly give your current 2.2uf Hovland caps ample time to break in to get the full measure of their sound. If you feel that after determining the bass roll-off point that you want a lower cut-off point, (assuming you like the overall sound of the Hovland), replace the 2.2uf value with a higher value single unit( not bypassed)Also, very important, you need to make sure that the voltage of the capacitor is equal or higher than the value supplied by the manufacturer. There is a wealth of information regarding DIY stuff on various forums in Audio Asylum. Doing a search there will give you many hours of reading and learning. Perhaps others more technically knowledgeable on electronics can make some suggestions for you. I am more an audiophile than a technician. My DIY is very amateurish and limited to some basic soldering in of caps and wire harnesses. Be careful but have fun. If by chance, after listening to your system once the Hovland caps are fully broken in and you still don't like their overall sound, you can always put back in the Auricaps and they also will improve with some burn-in time. I have found that most of the top polypro-type caps need at least 100 hours to fully form in your circuit to sound their best. Good caps are like new cables. They need time to break in. Patience is a virtue here.