Phono pre direct to amp, what am I missing?

I have only one source in my system (turntable) and don't plan on adding any others. I'm thinking of getting rid of my integrated amp and was curious about running my phono pre direct to a standalone amp. I guess my question is, what am I missing by not having another pre-amp in the middle? Is the pre-amp just acting as an expensive volume control knob when using only an external phono pre? if that's the case, I would rather spend more $ on the amp and maybe even upgrade my phono pre to the next level with the money I would have been spending on a pre-amp.
Depends on what equipment you have and your budget. There are a few phono stages with volume controls, E.A.R. 88pb and Aesthetix Io are 2 examples. Also there are preamps with built in phono stages (more common) Aesthetix Janus is one example Atm asphere MP3 is another. Plenty other examples i am sure...

I have never tried a straight to amp phono. I have tried it with digital and I prefer a preamp...
Most preamps also add between 10 and 20dB of gain, so it depends on the efficiency of your speakers and the gain of your phono preamp and cartridge as to whether or not you would have adequate gain to play at the volume level you like.

If you have reasonably efficient speakers and adequate gain between the cartridge and phono preamp then you could do it.
The worst that could happen is that you won't have enough gain when you hook it all up.

You might try a PS Audio GCPH because it offers volume control, muting, and polarity reversal via the remote control. And they can be bought between $500 and $600 on the used market. Just remember that you will need a volume control somewhere...
I already have the phono pre, I just want to know what I am missing by not having a $2000 pre-amp between the phono pre and the amp. it still sounds like it is only coming down to volume control and that the pre-amp actually does nothing to the sound of the phono pre?
If you have enough gain, and only want to run the phono stage, the only thing you're "missing" is a layer of coloration/distortion. One-source systems are tailor-made for running directly into the power amplifier, as long as, as has been mentioned by others, you have sufficient gain to get the listening levels that you want.
I run the Coincident Statement Phono directly into my monoblocks without issue.
it would be a K&K phono stage running into a yet to be determined tube amp, maybe a BAT or ARC.
also, how much total gain is needed to make things sound "right"? I mostly listen to rock based music at moderate levels.

12-24-11: Vortrex
also, how much total gain is needed to make things sound "right"?
It is not necessarily any needed gain. Sometimes there is just something else going on that makes it sound right. Maybe it is the blend of two components used together that make up for the others weakness. It could be a needed colorization that make them work together well. All gear is colored, in my opinion. I'd like to know why, but don't. I don't like extra components, or paying for them, especially if I don't need it. I'm just in the hobby, no money being made here. Try the direct approach, and if it sounds great, go for it.
A very fine linestage will usually improve tone and dynamics vs. running a source (in this case the phono pre + cartridge sourcde plus preliminary gain) even though with a linestage you are usually throwing away some of the system gain. But sometimes the right combination of phone pre + power amp can deliver sound that argues for eschewing the preamplifier.

Two things are critical: First as already mentioned by others, somewhere you need a volume control. The second is often overlooked in the gain chain: the input sensitivity of the power amplifier vs. the maximum clean output voltage of the source, before clipping.

Something an Audion power amp with 0.7v input sensitivity can be driven to full power without strain or dynamic clipping by almost any source (including the output of a phone preamp, but not including the output of a cartridge directly) without the extra boost of a preamp in the chain. On the other hand, some American power amps that have input sensitivity of 2v, 2.5v or more can't be driven to full power by the output signal of a source only able to output less before clipping. And an output spec of 2v isn't a guarantee that the analog output will sound best when operated at its limit. So get that relationship right, and you will at least not be shortchanging your power amp's available dynamic range, nor pushing your source's output into compression or clipping. Whether a preamp sounds tonally better in that case over no preamp, is up to you to decide for yourself.

Kevin from K&K did provide me some numbers before to use when looking for an amp if I wanted to go direct. I seem to have lost that email and don't remember what they were. I'll get back in touch with him, but assuming I have all the numbers in sync, I was mostly wondering what would the sound be like with only the phono pre.
He can also fit in his excellent stepped attenuator to his phono stage (which I also owned in the past) to provide you with the volume control you may need.