Best way to integrate a sub into 2 channel system?

I have looked at many of the threads relating to this subject but was unable to come away with any firm conclusion. I have a tube preamp and amp and bookshelf speakers plus an active sub. Please tell me if one of the following methods is considered best:
1) Use the high level connections(speaker wire) from the amp and then to the speakers using the sub's crossover

2) Use the low level connections (RCA) from my preamp to sub to amp using my sub's crossover

3) Buy an eternal crossover (Outlaw ICBM) and place it between my pream and amp to send the low freqs to the sub (low level connection/RCA) and high freqs to the amp. I know that I need to disable my subs crossover in this case.

With 2 and 3, I know that I would be relieving my amp of having to deal with the lower bass freqs and potentially improve the mids and highs but run the risk of the crossover causing problems.

thanks for the advice,

#3 Look into the Paradigm X-30 crossover...around $125 and does an excellent job.
What sub do you have?
My sub is a Definitive Technology TL15+
choice #2--that's the way to go. peace, warren
choice #2
Run a second speaker wire from your amp terminals to the high level inputs of the sub and stop there. Still run your speaker cables from your main amp to your main speakers and let them run full freq. In other words use the high level input on your sub but just don't use it as a crossover! You can use one set of speaker wire to the sub. cause everything under 100hz is mono anyway. If you use the sub as a crossover you ruin what good your amp is doing. The sub hooked up to the amps will blend much better than using a RCA out of your preamp. Try both ways and post your results.
Philefreak (or others),

would running speakers wire to the sub high level inputs and the main speakers be the same type of load for the amp? I would guess so but was not sure.
Greetings, Warrenh (as usual) and Aroc are right on regarding choice #2. You will get better integration and more headroom from your main amp using the subs X-over. I hope this helps. Happy Listening! John
Chris, using the high level inputs on your sub will change the load your amp "sees." It will lower the impedance and may cause your amp to run hotter and you will have less headroom than using choice #2. Listen to Warrenh and Aroc go with #2! Happy Listening! John
No, It will not be the same load for the amp. But, it's better to load the amp than the preamp. The amp will see a higher impedance, if your using a tube amp then the higher the better(with the exception of a few, Music Reference and Decware just to name a couple). If your using SS for amps then it's still just fine. The best preamps do not have a buffer output stage so, even if they have dual outputs, they're just parallel. This puts a load on the preamp out, that far more hurts the sound of the system than the amps... cause this way makes your impedance differ into your main amplifier and we don't want that.(course in some instances it may be better to alter the impedance into the main amps) If a preamp has a buffer output, then by all means use the second pre. out but, the pres. that have this buffer are not near as transparent and resolving(usaully entry level pres. or home theater stuff, this makes them more bullet proof but compromises the sound)) These are my opinions and thats all. There are some that would argue this with me but, in my room and my gear it always works best to hook the sub up high level to either the amp terminals or one of the main speaker binding post.Just try both ways, I've heard it work both ways actually but, in my room as I said before, it works best high level and for most of the people I know.
I think sugarbrie has asked a good question...I myself use choice #1. Previously I used choice #2, but I found that the crossover in my velodyne sub "dirtied" up the signal that was being sent back to the amp. I have seen this question asked a number of times in threads, and much to my suprise...many people on those threads were recommending choice #1...seems as there is a different school of thought here. This is just my opinion, I hope I'm not adding undue confusion so please everybody dont beat me up.

Then again...why not try it all ways and see what you like the best.

just my 2c

I went with choice number 2 and it worked out fine for me.
Thanks everyone for the advice. I am going to try it both ways and see what works best. My Preamp is a Bottleheas Forplay which, I think, can handle driving the sub. I just arranged to buy a used ICBM external xover here on Agon. At this point, I just need to hook up my system both ways to see if pulling off the low freq info before my amp improves the mids/highs without negitively affecting the sound too much due to the addition of the ICBM. Either way, it will be fun to experiment and I can always sell the ICBM if it doesn't work in my systmem.