Rega Planar 3, Parasound Halo pre, their 2125v2 amp. Upgrade:TT, cart, or poweramp?

This hobby will empty your bank account. I have been buying my dream system for the past 4 years. I have spent $105,000.00 and ended up with 3 systems. My main listening system on the main floor, the basement system for general listening while working on model railroad. And the garage system where all the leftover gear and cables went that I would not give away to grinders.  My main system, I have both digital and analog. I just placed an order for a Jeff spall Tonearm, another $2200.00 upgrade. I have a Rega P3 in the basement With a Goldring 2300 cart on it. 

I have a lot of Saturn audio equipment, some of the best for the price. I have the Saturn dac, power conditioner and Phono stage on my main system. I have the Saturn Power conditioner, and Aqua La-Voce S3 dac in the basement. 

End game amps, main floor Sugden MPA-4 pure class A mono blocks with Sugden LA-4 preamp. Basement system is the Sugden IA-4 integrated amp. 

I have a $6000.00 amp out in the garage. lol Arcam A-49. At this point the Garage /cigar lounge has $12,000.00 worth of audio gear in it.

Do yourself a favour, find an honest dealer and stick with him like I did., he won't steer you wrong. Stay off the forums, too man know it all experts who are cheap and have convinced themselves that cables don't matter etc. stay away from those people. make your own Journey. listen with your ears, and never settle for good enough. Settle when the music you are listening to makes you tingle inside.

I don't know what you income is and I don't care. Manage your life and finances so you can enjoy the hobby.

What’s the ratio of analog to digital in your listening?
Are you planning to keep buying records or will you be streaming more? The amp upgrade is an impact across the board.
These are some of the decision making factors.

Problem with having both digital and analog is you will be playing a whack-a-mole with each upgrade

Figure out first what your goal is and what you’re planning to focus on.

I like Halo but they are also very laid back, so depends on how you pair them with your music and speakers and room.

The problem with upgrading DACs and streamers is they are digital, so that means that in a couple of years or maybe three, new stuff will be out that will be better than what you just spent megabucks on.  I spent over $4K on a nice DAC, fempto clocking, 24 bit, 196KHz, but now fempto clocks are becoming common and the new stuff is 32 bit, 384KHz.   My DAC sounds damn good but I can see the new stuff is out there and the prices are falling, however slowly.

Given what you said, and what you implied based on your wording, I'd spring for a new cartridge and upgrade there first.  It is almost always more significant than a tonearm upgrade and your TT setup seems pretty good to begin with. 

The Parasound amps are very fine amplifiers, the Halo's are the top of their line, but the classic stuff is also very good.  I have the bigger classic than the one you have and I just bought another one for the subs. I use Conrad Johnson Premier Fives monoblock tube untis at 200W each for the mains and two stereo Parasound Classics for the four subs.  The combo is very hard to beat and I doubt I'd get much more performance going to the Halo at similar power levels.

Frankly, rather than put more money into "better" amplifiers, I would biamply your system first.   That always makes a huge improvement, way beyond what the extra amplifier costs.  Pickup a used crossover network or make one a passive one, and be amazed.