If you are looking for "better" in terms of performance spec between DAC-10H and DAC-9+HPA-9, there is no direct comparison.
DAC-9+HPA-9 is cheaper than DAC-10H mainly because DAC-10H is more costly to make due to the dual gain stage design.
Why dual gain stage?
Because it is designed as a do-it-all preamp and headphone amp that can match anything on the market. The gain setting affects the preamp output thus making it incredible versatile for any amp. So for DAC-10H, the emphasis is for exceptional preamp AND headphone amp matching.
And it uses the ESS9018 chip which is very neutral and clean.
DAC-9 uses the AKM chip that is slightly warmer and it lacks the preamp gain adjustment like the DAC-10H. The HPA-9 is incredibly good without the need for dual gain stage and due to a different design, it is able to drive any headphones even though the stated power is a fraction of the DAC-10H, spec doesn't tell the full story. Those of you who are technically incline can read the HPA-9 design on the product page. Those who want to know if HPA-9 can really drive anything, read the review on head-fi.org (which is also posted on this forum) by another user.
If your music preference is classical and Jazz, go with DAC-10H if you also play with different amps and speakers, otherwise consider DAC-10 + HPA-9.
If you prefer vocals and warmer sound, go with DAC-9 and HPA-9, but DAC-10 and HPA-9 will also work very well.