You would have an ideal set-up if you were to add a pair of Q500 floor standing and a Q200c center speaker. If you're in the US the Q500 are on sale for $700 a pair and the Q200c for $400, so well under budget.
The weak link at that point is your subwoofer. The Q400b is OK, but nowhere near what a good SVS, Hsu Research, or Rythmik sub would do for very little more money. If you paid list price for the Q400b those other companies have subs for the same money that outperform it.
Consider if you have that total $2100 available, spend $1100 on the Q500 & Q200c. Now you've got $1000 to get a more current receiver if you need (or anticipate needing) features such as Dolby Atmos, a higher level Audyssey, HDMI2.0, HDCP2.2 and more. Unless you need that, a better sub would be where I'd put that money.
KEF R500, R200C, R100, R50, SVS SB2000 sub, NAD T758v3 AVR, LG UP875 4K BlueRay, Samsung UN55JU6500F 4K LED TV, KEF M500 headphones, Sony CDP-CE500 CD changer. Office: NAD M10, KEF LS50, KEF Kube 10b, Pro-Ject RPM1 TT w/ Ortofon 2M Red. Guest room: Hafler 300 L-R, KEF Reference Model 100 center, KEF iQ10 surrounds, modded M&K V-90 sub, Bluesound Vault 2.