What is the purpose of an Amp? Do I need one for my setup? If so, why?

Depends on which Integra 9.9 you are referencing. If the DTR 9.9 then no, you will not need amping as that is a receiver. If the DHC 9.9 then yes, you will need amping as that is a preamp/processor. In that case, you simply use either unbalanced RCA type connections or XLRs for balanced (no hum issues) from the preouts on the processor to the amp channels. If the amp in question has gain knobs for each channel, simply turn them all the way up.

If the DTR 9.9 receiver has preouts (I suspect it does), you can still run external amping if desired. The benefits of external amping are generally better dynamics (with larger capacitance reserves), headroom (greater output/higher volume without compression, distortion effects), better Bass control, etc., especially with speaker sets with more challenging specs. A 4 Ohm speaker with low sensitivity (say anything under 86dB) will benefit more than a higher sensitivity (90+dB, 8 Ohm) speaker. Audible improvement is usually on the margins. Larger spaces will usually benefit from external amping as well.

Klipsch are usually very easy to drive. If the listening space is not too large, you should be fine with the DTR 9.9.

When setting up a home theater, there are two (and a half) ways to go:

1. A receiver, with all amplifiers built in. Most of us will be very happy and well served with such a setup. I'd guess that 90% of AVSers fit in this category.

2. A preamp/processor with separate, stand-alone amplifiers. This approach is preferred by tweakers, traders, always looking to upgrade guys (like me) who prefer an outboard amplifier for a variety of reasons, some quite valid and some quite questionable.

The half category is those that have a receiver and use preamp out jacks to use a separate amp or amps for some (typically fronts) or all channels. This approach is popular with people who bought a lees expensive receiver (read: low powered) and want to get a bit louder without throwing everything out and starting over.

If I were starting all over, I'd be very happy with a receiver and no need for outboard amplifiers. I strongly suspect your friend will, too.

The pre-out for Sub allows an internally powered sub to amplify the LFE signal ... or any Bass below the speaker crossover selection in the receiver. Preouts of any kind simply allow for external amplification of the channel in question and remove the amping duties from the receiver.

pre-out means line level (low voltage). While speaker out means amplified signal that goes to an otherwise unpowered speaker. The RCA outputs signify line level. Low frequency is much harder to drive than higher frequencies. So, receivers and even amps outsource this job to dedicated amps that reside in the subwoofer box itself. So, they send a line level pre-out signal to the powered amp. Most subwoofer also have speaker level inputs.