For A while I just linked my DCT641x/341x,6 to my PC via Firewire and saved the raw TS Streams on my Own PC. then played back in VLC at full 1080i no issues.
The DCTx(3/6)41X(2/6)s support 1.0TB drives, however the IPG version Cox has would re-write the partition to 160GB on first boot after installing the 1tb drive kit.
Cox made it easier with cable cards, we are no longer restricted to Motorola's Hardware.
Ceton has PC tuners that work fabulously inside of HTPCs ($199, Cable Card Ready, 4 Tuners, Software to setup individual tuners as Network tuners (So you can leave the HTPC next to your main TV, but still access the tuners in it from another PC Via Network)). I Know several people that have these as I've built the units for them locally, and they work fantastically, not sure if OnDemand works, but a system running Windows 7 can simply Minimize Media center and goto HBOGo/MaxGo or Cox.com/TV
Storage Space is limited by the HDD size and not IPG Partition Size.
Not to mention media Center has more options than the Motorola Units(internet TV, DVD/BluRay, Shared Video/Images from All Networked PCs etc).
I will be building one for My house this summer to replace 2 DVRs that are both Limited to 2 tuners/160GB each. and Since i do 99% of my work on my PC and watch everything on my PC, I can just set 1 of the 4 tuners to be my tuner over the network, open WMC on my PC and have tv on my PC.
I was happily building them for my friends that live in my area (i built 3 a few months ago).
$400-600 depending on components and HDD size vs $300 Retail For a DCT 341x/641x box from Motorola vs $42/Month ($504/yr) to rent 2 from cox.